It really comes down to what monitor you'll be using - if you will use a high refresh rate monitor, i.e., 144 Hz or greater, then it's best you wait till October 5 for Coffee Lake CPUs to launch, and get an Intel i7 8700K. If you will be using a 60-120 Hz monitor only, then a Ryzen 7 1700X would be the CPU I'd recommend.
This is mainly because high refresh rate gaming requires strong per core performance, which is found mostly on Intel chips. For a 60 Hz monitor, you don't need very strong per core performance, so a Ryzen CPU is also sufficient. Since a Ryzen CPU has better value and more cores for the same amount as an Intel chip, Ryzen CPU becomes the better choice for a 60-120 Hz monitor.
So, depending on the monitor you have, you'll have to decide yourself as to which processor is better for you - Ryzen 7 or the upcoming 8700K. Avoid the 7700K, it isn't as future proof, and a quad core will really be the entry level for gaming in some time.