Nothing is good to CPU mine because botnets would mine it and dump it to below electric costs. GPU mining is barely profitable anymore. If you want to get into crypto you are probably going to want to either just buy the coins or buy an asic for scrypt coins or a GPU for asic resistant coins.
Well, I have lots of free credit on Amazon and DO for virtual servers. So at this point, my mining costs would be 0, anything I make would be considered profit. Do you mean botnets would lower its value? Which GPU should I buy? I don't want to get a top of the line ultra costly GPU. If I'm understanding it correctly, bitcoin exchanges operate similarly to stock exchanges, right? I have my computers running 24x7 anyway, so mining doesn't cost me more than running my computers already does.