If you have a definite spending limit, here are your best options
Putting together a new system tends to begin with selecting a the processor that fits your budget best, narrowing down make, performance and price until you have the one you need. What are the best CPUs on the market right now, though? The industry evolves constantly; so are Intel chips still better than AMDs? Which of Intel's platforms is the best? Should you buy an FX-series CPU or a Fusion APU? These questions and more will be answered in our guide to the best current-gen CPUs on the market right now.
UNDER £50
Intel Pentium G3240 (£43)
The cheapest Haswell CPU worth buying, the Haswell G3240 is a dual-core Pentium clocked at 3.1GHz. A cut down version of the Intel Core chips, Pentiums differ in a few ways: there's no Hyper-Threading on any dual-core Pentium, only 3MB of level 3 cache, and they contain Intel HD Graphics GT1 GPUs, which is only half as good as the HD Graphics 4600 chips found on higher-end Haswells. The G3240 supports dual-channel RAM up to DDR3-1333, but all others support up to DDR3-1600.
Designed for use in office and low-end systems, Pentium chips don't represent particularly good value, but they're also the fastest chip you can buy new under £50. That said, don't expect to get much graphical performance out of them unless you're pairing them with a decent graphics card - their GPU is designed for office use only.
If you're building a budget system, the best reason to buy a Haswell Pentium over any other chip is that it's potentially compatible with Broadwell chips further down the upgrade line. The G3240 is a Socket 1150 CPU, so pair it with an Intel Series 9 board and you could potentially swap in anything up to a Core i7 Broadwell chip at some point in the future. It might be the bottom rung, but at least it does get you on a ladder that could carry you a lot higher when need dictates or budgets allow you to do a little bit of climbing.
AMD A6-7400K (£45)
The AMD A6-7400K is a Kaveri-based APU that uses the FM2+ socket, with six cores clocked at 3.5GHz. The retail price is actually somewhere above £50, but it is possible to find it cheaper without much difficulty.
AMD's low-price chips are arguably superior to Intel's when it comes to building a powerful system, as long as that system isn't intended for gaming use. Indeed, the A6-7400K compares quite favourably with the Pentium G3240. Multi-core performance is about the same and single-core performance is slightly lower, but the Radeon R5 graphics chip is far superior to the Pentium's on-board version and it supports DDR3 up to 1866MHz. Although the TDP is about 10 watts higher, so be aware of that if you're building a low-power system.
The thing that really makes the A6-4700K worth considering, though, is that it can be overclocked. Done right, this will push performance up above the Pentium without much difficulty, giving you a better return on your money. If you're looking for a cheap gaming system, this ability - combined with a better GPU - is your best chance at getting one with a CPU under £50, unless you want to buy a graphics card too.
UNDER £100
Intel Core i3-4160 (£90)
Intel's Haswell CPUs are great for gaming, but chips in the core line are expensive and it's often tough to tell whether you're getting a good balance of price and performance. That's not the case with the i3-4160, which hit shelves in July 2014 and quickly proved itself to be a well-refined competitor to other Core i3 and Core i5 chips, standing out instantly thanks to its solid performance and low price. Anyone trying to build a gaming or media system on a budget would do well to consider it, especially if you're wedded to the idea of buying Intel rather than AMD.
This dual-core chip has a 3.6GHz clock speed, two hardware cores, on-board Intel HD Graphics 4400 and a pleasingly low TDP of just 54 watts. Although it can't be overclocked thanks to locked multipliers, benchmarks show that Hyper-Threading gives it gaming prowess beyond the suggestion of its model number and price. It's one of the best value Core i3s that Intel can offer, and for the sake of a few quid it's worth going with the faster version over any other.
Be warned that varying availability means you might find some slightly worse chips at a higher price than the i3-4160. In particular, the Intel Core T-series chips are cherry-picked for low power performance, but this selection process adds a few quid onto their price. The Core i3 4130T, 4150T and 4160T are all easily found for more than the vanilla 4160, but that's because batches with low power ratings are rarer. Unless you're desperate to save a few watts on the TDP, go for a vanilla 4160 instead.
AMD A10-7800 (£99)
Brushing right up against the bracket for our intermediate budget, the A10-78800 is a 3.5GHz FM2+ Kaveri APU with 12 cores, a 65 watt TDP and support for DDR3 up to 2133MHz. Again, it matches its Intel equivalent quite closely in a number of areas. The Core i3-4160 has the edge when it comes to single-core performance, but multi-core performance is actually a little better on the AMD chip.
This AMD isn't unlocked, though, so you won't squeeze any extra performance out of it - and it's 10% more expensive without being 10% better. The FM2+ socket does mean you could upgrade to a Carrizo chip in a few months, but if you're planning on that, we'd just to wait for the new line to be released.
Again, the best reason to consider the AMD chip over the Intel one is its GPU. It's so much better (a Radeon R7, in this case) that if you're trying to make a gaming system without a stand-alone graphics card, you'd be better off with the AMD. As an all-rounder, however, it starts to noticeably struggle against Intel's chips, and that trend only gets worse. Unless you're a staunch AMD supporter, this is the best AMD chip we can actively recommend.
UNDER £200
Intel Core i5 4690K (£192)
First seen on shelves in June 2014, the quad-core i5-4690K has a 3.5GHz base rate that's 100MHz faster than Intel's previous best i5, June 2013's 4670K. That translates to better single-core performance and slightly better value than the older chip, which makes it more than worth tracking down instead. The 4690K has a TDP of just 88 watts and on-board Intel HD Graphics 4600, though if you're buying it for a gaming or media editing system you'll want a proper graphics card in there.
The main advantage with the К-series chips is their overclocking capabilities, and if that's what you're looking for then it's a good idea to go for the latest, fastest chip in the Core i5 line. The newer materials will stand up to that little bit more stress. Obviously, if you want a faster Haswell chip you could look at the Core i7 series, but for single-threaded tasks (like gaming) there's very little advantage to be had by paying extra. In any case, once you start buying in that price bracket the performance you get per pound starts to drop significantly. The Core i5-4690K is, by far, the gaming chip with the best speeds for the best price.
Remember, too, that if you're definitely not planning to overclock your chip you can save around a tenner by going for the locked version (without the К suffix), and it's probably worth doing that - the selling point of К-series chips is their overclocking potential and if you know you won't exploit it, don't waste your money.
AMD A10 7850K (£130)
At the very top tier for AMD's А-series chips, the quad-core, multiplier-unlocked 3.7GHz A10-7850K is currently priced at £130 - about half the amount that Intel's top-end Haswell Core chips cost. That, if nothing else, illustrates the scale by which AMD and Intel's performance differ. This is as good as AMD gets, and it's not even competing with Intel's mid-range core chips: the closest-priced Haswell CPU is the Core i3-4350, which is the fastest Core i3 chip and slightly cheaper than the A10. If your budget is up to £200, you can't do any better than this for an AMD chip without going for an older CPU.
Again, what makes Kaveri attractive isn't its single-thread performance, but the superior graphics capabilities. Again, the AMD chip has an R7 GPU which is outright superb compared to Intel's HD Graphics 4600 - though if you're building a mid-level gaming PC, it's unlikely you're looking to buy a Core i3 without a graphics card. Literally the only useful thing the AMD chip does that the equivalent Intel doesn't is support 2133MHz RAM.
The A10 7850K is unlocked, so there's a little more performance to find within it, but even then it's struggling to match Intel's line. AMD might put up a reasonable fight when you're building a budget system, but if you want one that'll handle the strains of high-definition gaming or entertainment, this isn't really the option to go for. Either way you need a graphics card, and once you've hit that point, Intel has the edge in performance, price and upgradeability terms.
OVER £200
Intel Core i7-4790K (£275)
Intel's most expensive Haswell chip is actually the Haswell-E i7-5960X - an eight-core 3GHz chip (16-core with Hyper-Threading) that costs no less than £850. It is, of course, so expensive that buying one for a desktop system can't really be called the act of a sane person.
If you're going to go for a high-end Haswell chip - and let's face it, if you're trying to get the best PC, you want to - you should probably stick to the more affordable regions of the standard Haswell platform. The Intel Core i7-4790K is a 4GHz quad-core CPU with Hyper-Threading, and the fastest in the standard Haswell line. It doesn't outperform the i5-4670K as much as you might think, but it does outperform it, and in a battle of sheer power that's all that matters. The only downside is that it's a lot worse in terms of performance per pound, but that's been a standard problem with the Core i7 line ever since it was introduced. They're not CPUs for people who are scrimping.
The fact that the 4790K is unlocked does mean you can squeeze a little more performance out of it as long as you have a sufficiently good cooler, but we wouldn't recommend that as a strategy. Unlike Core i5 chips, Core i7s are already operating at their limits, so it takes some heavy-duty hardware to get them past it by any significant proportion.
AMD FX-9590 (£200)
As we've previously discussed, AMD's Kaveri APUs don't go past £130, but let's imagine that you want a high-end AMD chip for your budget of more than £200. What can you get?
In this case, your only real option is the last-gen Piledriver-based FX-serious chip, which has no on-die GPU. An eight-core chip clocked at 4.7GHz, it's the fastest FX-series AMD manufacture, and probably always will be, since the FX-series seems to be dead now.
On the plus side, it's the first AMD CPU in years that can actually hold its own on gaming systems (if you have a graphics card, otherwise it's useless) but there's a slight problem in that it's still vastly underperforming for its price. It competes with Intel Core i5 chips like the 4670K, rather than the similarly priced Intel Core i7s, and it still loses out to them - the even without overclocking, the i5-4670K is substantially better at single-core processing. The FX-9590 also consumes almost three times more power than the i5, isn't any better at running multi-threaded software, and it runs on a CPU socket (AM3+) which is essentially dead, making it an expensive investment in a system with only a short lifespan left.
The only reason to even look at this chip is if you own an AM3+ system already and aren't willing to upgrade. For £200, though, we'd be tempted to suggest you just buy an Intel board and CPU instead. It's no surprise, when you look at the FX-9590, that AMD refocused its desktop line around budget APUs. It's simply not in the same league as Intel's chips.