If you want the best follower, I'd say go with Serana. Not only because she's a cool vampire with HP-drain ability, but because she have a different AI than the rest and she's more alive. For example, when you bring other followers, they'll be just stand there staring at you 24/7. Who does that? But Serana, she interact with the props around you, like, sit on a bench and drink, cook on a campfire, etc.

I'm telling you this because maybe that's something you don't really remember too, so..