the AMD APU will be better for gaming in a non desecrate GPU situation. Intels current generation (skylake) iGPU is capable of accelerating 4k video decoding, i do not know about AMD's APU's. You will be running your games at 1280x720 if your looking to get playable frame rates from either, so it wont be anything good looking on a 4k display.
im taking a guess you have a 4k display if your asking about 4k playback (well, UHD). does this display support Display Port or is it HDMI only? (AMD hardware at this time does not support HDMI 2.0 which is a deal breaker for many)