Engineer. You are basically throwing all game mechanics out the window and saying "Fuck it, I'm just going to build an aimbot to do all the work for me." It's so mindless from what I've played and seen from it. I know there are engineer mains that do some really impressive things but I'm going off of what I see when I play on an average server.
I don't like pyros either. They're pretty easy to kill too. Even if they know how to decently reflect a rocket, I can still manage to take one out. They're just pointless, I mean, I still get nice killstreaks with a pyro. My loadouts are the phlog, scorch shot, and the powerjack. My second loadout is the degreaser, flare gun, and axtinguisher. My third is the degreaser, reserve shooter, and the powerjack.
All i like in certain ways, however if i had to pick a least favorite i would go with the medic even though im pretty good at it
Just find what weapons work for you as spy and how you play it, like I use the clock and dager because I like to wait for people to come by.