If I was building a system right now out of those two for gaming I'd go with Ryzen 3600. You'd get an unnoticeable advantage in a few games from Intel, but going forwards you're getting double the threads from Ryzen.
Heres a good review pay attention to the minimum frames rather then the average.
Understand that you'll notice dips more then 3 or 4 fps less average. Bad commentary from me there, shouldnt post in a rush. While the statement is true the 3600 is basically level on average with the 9600K according to Gamers Nexus
Heres TPU's results as well, they present an average across their whole suite of games, 10 in this case. At 2560x1440 the difference is less then 1% on average in Intels favour, at 1080p its less then 5 %. In non gaming tests the I5 offers 88% of the performance.
Just to clarify for you. I currently have an Intel 7700K, it was the best option at the time I bought it. I havent had an AMD CPU since a Duron 800 20 years ago. They are currently by far the best option as essentially they are offering comparable single thread (Per core) performance but with potentially double the overall performance (12 threads vs 6) for less money then Intel.