Well it depends if you want to go all out or not. If you want to make sure you are alleviating a bottleneck, then you want to get something with more Throughput for gaming, I.E Clock Speed over Instructions Per Second, unless you are not doing gaming, and need something to handle lots of bandwidth, in which case you would probably need more cores, and better power delivery, in order to ensure stability. Of course, then you need to consider AMD over Intel, and which Motherboard you have Already(assuming you have one.) If you have AMD and need to Game the Ryzen 5 3600X or XT is probably better because of the higher Clock Speed. If you need more Bandwidth Available, then you should probably get a Ryzen 7 3800X.
For Intel(Not that I would)...