Slippy, purely because this one scene from Lylat Wars (Star Fox 64). Stupid frog.
Also how could you miss off Roman from GTA IV?
On the Adoring Fan: I thought he was great, he served as a quick and easy way to get contacted by the darkbrotherhood. Most people kill him straight away so the numerous hours you spend in game are free from his presence. Plus all those funny kill him videos were always great to watch.
The adoring fan was one of my favorite parts about oblivion, the dog was an essential part of the game, Navi was useful, Slippy taught me that everythings better with barrel rolls and I've never played a J&D game, so I can't say.
For some reason I always seem to like sidekicks more than main characters.
I was never bothered by the Adoring Fan... I just took him somewhere obscure, told him to wait there and never went back for him. Same with Fallout 3 - I currently have Dogmeat, Fawkes and Star Paladin Cross hanging around at my house in Megaton.
My choice is not any one person, but a game. GTA4. All the escort missions, all the between-missions pissing around with your friends... it was a massive waste of time. I reckon they count as sidekicks, albeit loosely.
Definitaly Navi, although more people seem to be picking The Adoring Fan. I feel that The Adoring Fan was part of the fun of Oblivion, you could shoot him off the tallest peak, lure hime into a dungeon and cast invisibility on yourself, and many other other amusing murders. You couldn't really do that with Navi, making her just plain annoying and useless and The Adoring Fan, something the Devs threw in because they knew people would want to kill him.