Scout: IMHO the bestest is pickled. Violent Videogames and Laser Shark are up there too. But none of them are in eGO. I'm going to have to say xyrior. VP is good, no doubt. But I don't change how I play knowing he's out there...and I do for xyrior.
Pyro: Drywin.
Soldier: Wilson. Bigwilly. Wronskain.
Demo: 2di4u. SnowCanary. Fubie.
Heavy: MentalBuga. bugabugabugabugabugabugabugabugabuga
Engy: PurpleHuskies. Haven't seen him in a while though.
Medic: I'mma think on this.
Sniper: Cornbeefand$%*&@#rice! Her and that lucksman would make me rage! Haven't seen her in a while either though
Spy: Quantum was the only one who would ever drive me nuts. I suppose going up against him made me get good at pyro. Nothing against strabes & curly, but they don't make me rage the way Qua did.
Please don't take any of this as me poo-pooing anyone's skill, or touting my own. There's plenty of good players I didn't mention. There's even some who didn't make this list (Dimenhydrinate, Chelsam) just because they aren't in eGO. But there's only a handful who make me change my tactics, or my loadout, or my class, or my team; knowing I might run into them.