I've actually got the same question. I'm planning to build a new gaming rig right now and I'm torn between the i5-4690/k or the i5-6600/k (my old one had a C2Q Q8400 so either will be an upgrade nonetheless). I've been scouring the net for answers but it just made me more confused. Some people in reddit are saying to go with Skylake since its future proofing, it has significant "tock" performance gains, and so on, but the others are saying to choose Haswell because there aren't much gains as believed, ddr4's are much more expensive but only marginally better if not equal to ddr3s, save the money and buy bigger GPUs instead, etcetc.
The 6600k is $50 more expensive than the 4690k where I live ($290 vs. $240). Which one should I go for?
Also, the reason why the "/k" is because I'm not sure if I am going to overclock at all since I don't know how (but I'm open to trying if it isn't difficult to do.)