Sniper because its OP.
The Heavy. It is the only class I really play. Since I was a child I have ALWAYS favored going in guns ablazin' over tactics and/or stealth. The Heavy is the embodiment of that class in my opinion. I love simply moving forward, mini-gun spinning, Heavy Weapons Guy screaming "Cry some more!!!" and mowing down 6-12 people in a row. Nothing beats that for me.
And then a spy comes up and does what spies do.

