I'm good at Engineer, or Scout, but I try different classes when I feel like it.
I also like playing as Demoman with the sword and shield and special boots equipped, it's hilarious. But no ranged weapon slot left. it's like a new class, which is the whole point.
And I want to get better at Spy, it's cool to be a good spy. I've managed to run around like I'm a soldier guarding a capture point and gotten medics to heal me but it's hard to actually get behind them and stab them then.
AND I enjoy playing Engineer and hitting spies with my wrench.