Favorite vanilla companion is definitely Star Paladin Cross, I like how she first escorted James across the wasteland and now she escorts you across the wasteland. She's got a good story line.
Are you actually serious? Cross if by far the most boring, judgemental person in the game. She never wants to be funny, and the only time she wants to speak to me is when she feels like passing criticism or claiming what Dad would have thought about my actions. Bah!
Though, I respect your opinion, and she is actually a good fighter. But I had no problem performing her execution -- a grand day, indeed.
Anyway, my favourite follower is definitely Jericho. I've only actually ever used him once -- my current playthrough, but he's been my character's best buddy ever since he entered Megaton, where our ex-raider friend tried to help him screw over Moriarty.
Great with a Minigun, too. Or a Flamer for up close.
My second favourite is Clover. She's hot, funny, and genuinely loves me. What more could you ask for?
Butch is up there, but I hate how he kind of thinks he's the leader, and whines when I try to take control of him. He's a good fighter, though, and a valuable assest to my team.