Voted rogue.
If you ever play a game with well implemented rogues, it's incredibly fun, especially if you get to kill other players with them (or at least have a live DM). And if a game ever lets you freaking steal from other players? It's so ridiculously fun. Stealth is also an extremely fun ability, and being a little bit squishy keeps you on your toes.
But rogues are often victimized by poor game design and end up overshadowed by the other classes. Probably the best gameplay potential of any class, but only rarely done well in CRPGs.
Clerics are awesome, but can also be victimized by poor game design where they end up as heal bitches. But as bit of a hybrid class, they have some of the most interesting gameplay in a party setting and thematically, they're superb, especially if you get to root out heresy.
Clerics are getting corrupted lately though, unless they worship evil and/or foreign gods they need to stick to blunt weapons.
Fighters, not much needs to be said about this classic archetype. They're the line holders and the backbone of your party. I prefer to have three or four.
Rules don't make them as interesting as they could be much of the time though, as weapon modeling tends to be very simplified and boring, when it could be really interesting if they took the effectiveness of each weapon type vs each armor into more consideration, as well as the defensive effects of each weapon.
Not the most exciting to play solo, but I always want 3-5 in my party.
Wizards however, ruin everything and shouldn't exist as PCs in their classic form. At lower levels, everything is based around protecting the 4 hp wizard, at higher levels they tend to get so overpowered that they overshadow the other classes significantly.
Wizards should be rare NPC villains, arcane casters in the party should be more well balanced and thus wouldn't need to be limited to robes and a stick and d4 hit dice.