Um... I suppose all classes have their uniqueness and I like all in some way, but I HATE Engineer's play style. (I mean the vanilla style.) I enjoy playing with the frontier justice, coupled with the gunslinger to be an offensive styled one but all in all it's a lazy and boring class.
Scout: I like being able to run fast and get up close to get those deadly hits on lower health players and being able to deal max damage to higher health classes, such as Heavy.
Heavy: I like being able to shred anything in my path and having a large ammo pool..Oh and eating endless amount of sandvich's.
Sniper: Well, its sniper.