Should I buy 3200MHz or 3600MHz RAM?

Anything above 3200 is considered overclocking and that’s up to your motherboard and/or processor. 3200MHz CL14 RAM would be a "better" choice over 3600MHz CL16. While Ryzen does like fast RAM, its only to a point. At 3200MHz the speed gain itself likely wont be significant enough to warrant the increase in latency.