this is where tweaking comes in, to maximize the hash rate while reducing power consumption, but, at lest when I got out of it, the best coin to mine if you did not have an asic was Ethereum as gpu mining for bitcoin was at that point, simply not worth it, unless you had multiple gpu to do so, and your power was not costly per kwh type deal, cpu mining for any alt coin that I know of, has long been pointless as gpu especially AMD ones are SO much faster, more power used, yes, but when the given hash rate is magnitudes faster it makes sense.
Maybe some gpu depending on power consumed and the much faster performance many of them now have (example R9 290 RX 480/580, R9 Fury etc) it maybe means they actually turn a profit, however, unless it is for specific alt coins that are ASIC proof (that is, ASIC are unable to hash the workload) ASIC are far far faster and average much much less power consumed, so therefore GPU mining for the most part can be done, but compared to something built for that purpose alone it almost is not worth it, now, if you had 2 gpu, 1 was for gaming, and the other was for mining in the same machine at the same time type deal, that is its own thing as well.
