The answer is that 'it depends'. The comment from Nerada is more based on the fact that there are some very strong 4* Eddies that when upgraded to 4* are very strong. I think you'll find for many 4 and 5* drops, that (apart from the really rare and super powerful chars) which is best really depends on what you are up against. There are cases where Iron Eddie (a 4*) is so much more useful than many other Eddies, for example.