There hasn't been much progress on the CPU since Sandy Bridge back in 2011. You can move to the HEDT segment and have more cores at lower frequency or stay in the enthusiast/mainstream segment. The real changes since SB have been on the chipset side. SB has no USB 3, only 2 bugged SATA 6Gb/s ports, no M.2, no U.2, and the memory controller is poorly tuned and has much lower bandwidth.
Having upgraded from an i7-2600K / Z68 through each series to my current i7-6700K / Z170, I can safely say the i7-2600K / Z68 combo was the most stable and highest quality. It was a GREAT combo and the best Intel has done since the first i7-9xx series with X58. It however lacks many features i actively use on the Skylake build such as M.2, USB 3, 6 SATA ports of which I use 4, and USB BIOS Flashback (ASUS). It is all about feature assessment, needs, and balance. No right answer here.