The returns from CPU mining are really low. The advantage is you can use your existing PC(s) and not buy anything.

Tom's Hardware did a list for GPUs:

https://www.tomshardware.com/best-picks/best-mining-gpus-ben...

"Which cryptocurrency" will also vary over time since the prices are all over the place, but that's the other advantage of not-ASICs. You can switch to whichever one pays better this month.