Best class for TF2?

What class do you go for most of the time when playing Team Fortress 2? I usually choose the Pyro - he annihilates scouts of the opposing team, deals some instant & lots of passive damage when at close range, easy to get assists on populated servers and can be a very useful asset when ubercharged for the whole team. Only downside: short range and not very useful on servers with only a few people. It's a shame that snipers are so crap on this game; I usually go sniping in multiplayer games but not with TF2. In this game, unless you have the support of other players at all times, it is very difficult to score any kills and there aren't any good sniping positions. Oh Battlefield 2 my beloved, one of the best games for snipers like me.

What's your favourite class and why?