Selecting a CPU can be a very emotional decision. I know people that swear by AMD processors and those that swear by Intel. At one point there was a clear advantage to AMD in the pre-Pentium days when the AMD x86 chips could perform many operations in fewer clock cycles than the original Intel chips. Since then the line has become very blurred. Each new generation of chip is faster and the chipset to support each new generation offers more and more for the board manufacturer.
Both AMD with their Black product line and Intel with their K stock numbers have surrendered to the overclockers since both of these have the overclocking inhibitors disabled and are marketed specifically to the hobbyist overclocking community. So no differentiation there.
Right now there is a year between when Intel releases their new generation of CPU and when AMD also does so and we are in the time between when Intel has released and before AMD will release. Generally for computer building hobbyists this has been an uninteresting time. For the last several releases Intel released chips for laptop use with each new generation and then for desktop use about the same time that AMD was releasing theirs.
This time Intel decided to shake things up. First they announced that with the sixth generation core chips that they would move from a two year development cycle to a three year cycle. If you want to know more about this you should be able to find many articles on this using your favorite search engine. The reason for the change though does not have any impact on my CPU decision. Second Intel announced that they would be shipping desktop CPUs first and that the laptop versions would come later. This is a big impact though since there will be nearly a year before AMD's chips become available for the computer hobbyist.
So if you want the latest and greatest the only choice today is the Intel CPU. Fortunately there are other reasons to go with Intel instead of waiting.
The product development name for the sixth generation core CPUs from Intel is Skylake. The Skylake CPUs use less power than the early marketing materials claim for the next generation from AMD. For example the third generation i5-3470 that I am using is rated at 77w normal power consumption. The sixth generation i7-6700 is rated at 65w for the more powerful processor that is 0.2 GHz faster.
Power has a direct relation to heat and heat impacts overclocking and chip life. The Skylake CPUs even use less power than previous generations of Intel's core line of CPUs. Also since Intel has deliberately kept the mounting specifications for the LGA-115x line of CPU sockets the same. So existing cooling solutions will continue to work and will have an easier time keeping the CPUs cool than they have in the past.
So the question now is i3, i5 or i7 and which model withing those lines.
the i3, i5 and i7 denote how many parallel cores and how many threads each core can process independently. i3 has the fewest and i7 the most. Since the plan is to overclock there is no need to look at anything but the 'K' models. This limits the decision to i5-6600K and i7-6700K. Currently there is a $105 average difference in the price between the two.
For my use the decision has to be the i7-6700K. Last night I did a test render of a single frame for a potential 3D animation project. It took 15 minutes with the third generation i5 processor. Simply moving to a third generation i7 would have cut this down to 10 minutes given benchmarks that I have seen. Intel advertises that the sixth generation CPUs are 2.5x the processors of five years ago. I prefer the more conservative estimate of 40-50% faster. So that test render would have taken 6-7 minutes. In practical terms this would mean that a minute of animation would take 6-7 hours instead of 15 hours. This is very important to me.
For gamers most of the difference between the i5 and i7 can not be measured. For those that play certain extreme games there is a big difference. Take that into consideration when you choose.
Conclusion: Use the Intel i7-6700K. If you want to save money you can use the i5-6600K and still benefit from the rest of this series.
Next in the series: Selecting a Motherboard and Memory