I've found that it's much much easier to reflect on those groups who may have had a few signature 'hits' than it is all time favorite band trying to pick one. As an example a guy could put on Paranoid last night and then an hour later find himself stuck on Heaven and Hell . And then the entire lead vocalists back and forth kicks in when deciding, and then an hour later you find yourself listening to solo careers by each and forgetting what you were looking for. For the record I could beat up Godzirra when listening to Neon Nights by Dio. It's been a very long day. I'm now going to play Planet Caravan on a loop and pretend it's Friday.