I7 7700k is king for gaming no question. Bad thing with Intel though is they normally change sockets when they go to a new cpu.
What are you planning to do with the system? If gaming, i7 will be a little better. But the 1800x is still going to do well. If you are doing multiple things at once, the 1800x is going to do better at that and workstation tasks. Depending on your budget, a lot of reviews say if you go ryzen 7 look at the 1700 and overclock it. Still 8 core, but you save some money with it. Most Ryzen chips seem to get a wall at about 4 GHz, some get lucky and get 4.1 or so.
The advantage and will have is that supposedly they will support the am4 socket until 2020. So you may be able to drop a better chip in there in 2 or 3 years.
Depending on your budget, you may also take a hard look at the R5 1600. It's 6 core and 12 thread instead of 8 core 16 thread. So you get a lot of the performance of the r7, but save a little that can go into a better GPU which will make not difference in gaming than the cpu.