[MetalMilitia]

I don't think there is a best class, as each class has a role which is tailored to suit a specific task within the team. Although it could be argued that there are best classes for specific maps (depending on if you're attacking or defending). For example the best class in Well is the Soldier.

The demo man is a pretty good all-rounder because the sticky bombs are perfect for taking out sentry and defending cap points, but without any real direct fire weapon they make easy targets for scouts and alike.

It could also be said that the medic is the best class because you can support the front line giving your team the ability to keep constant pressure on a cap point.

I would also disagree that the sniper is the best class. I don't think I've ever seen a game which has been won based on the actions of a sniper, whereas a good spy or medic/heavy combo can completely destroy an enemy cap point. The only level I can think of in which a sniper can make a real difference is the last stage/last cap point of dustbowl.