I’ve built many a PC and sold many a PC, I have a couple cents to share.
If you’re on a budget, go for and AMD 8 core. The motherboard for this will also cost less.
If you’ve got more money, go for an i7, don’t settle for less, dat hyper-threading…
On the AMD side there are several different versions of their 8core CPU, most all of them identical architecture wise and the only differences are the standard quality of silicon (to a degree) and the clock speeds. I’d try and go with an 8370 which has better grade silicon than a 8350 and is pretty much an under-clocked 9570/9590.
But seriously, overclock the crap out of that thing. a nice air cooler or a decent water cooler will take you to 5 GHz at about 1.5 volts. You’ll want the best chip-set available to the am3+ socket though.
I personally owned the 8370 for a little while, and I was pretty happy with it.
On the intel side, i7s all the way!!! I got the 5820k and I FREAKING love it, but a 4790k or whatever will be pretty dang good still and you wont have to pay more for the DDR4 and new socket that the 5xxx series chips need.
The 4790k is a solid chip, preforms great, overclocks well, good power usage, gamer’s dream.
GPU wise, I did a LOT of testing with an R9-390x, 980ti, and TitanX recently and I got to say the 390x was a pretty solid player, OpenCL is promising in Cycles and seems to be preforming better for geometry, but there are a few features unsupported and a few certain things will take longer to render in OpenCL than CUDA.
Get an r9 380 at least on the AMD side.
GTX 970 at least on the Nvidia side.
Which company depends on if you’re willing to work with openCL while it’s being ironed out. Keep in mind though that the 380 has 8GB of VRAM, which is pretty neat!
If you got the money, get the best you can, and that means intel. For the best experience, you’ll probably want Nvidia.