If you're buying now, the only option IMO is Kaby Lake, since it does both 8-bit SDR and 10-bit HDR in hardware. Skylake only does 8-bit. Furthermore, while any machine theoretically can decode 10-bit HDR 4K HEVC in software with High Sierra, none of them are fast enough to do it. Even an iMac Skylake Core i7 6700K chokes on 10-bit 4K HEVC. Stutter, stutter. The Skylake MacBook Pros don't even have a chance for the more complex stuff, even at 100% CPU usage. (Meanwhile, I can do it on my Kaby Lake MacBook Core m3, with under 25% CPU usage.)
Plus Kaby Lake has the hardware for Netflix 4K DRM, should Apple and Netflix ever decide to implement it using this method. Skylake doesn't not have this tech.