Fighters are very much at the top of the game. They have the perfect balance of offense, defense, and control.

Wardens seem to me to be second best. They have interesting control mechanics, a good marking ability, and decent control, but they aren't as good at punishing broken marks as fighters.

Swordmage is the only one I haven't seen in play, but they look like they can either be very controlly or very strikey. While they only start being able to mark 1 creature, with feats the can mark 2 at paragon, and all with in 2 squares at epic (bigger range if the took wandering swordmage PP and have decent wis). Positioning matters way less for them to benefit from their mark which leaves them to mark 1 enemy and engage with another. Power choice also matters a LOT for them.

Paladins are a sub par defender and a sub par leader. That said, they are an amazing 5th wheel in a party that has the basics covered. I consider their mark by far the least impressive, mostly because of the conditionalness of it and the slow scaling (especially if you take the STR build). It's only redeeming quality is that it always hits.