Favorites are Levitate and Technician. Both are very useful on my team.
As for ones I don't like, I'm gonna split them into two categories.
Truant, Klutz, and Slow Start are hindrances that make otherwise good Pokemon unusable.
I hate going up against Pokemon with Intimidate, Sturdy (5th gen), Static, Poison Point, and Effect Spore. It's just frustrating having to put up with random status effects or not KOing Pokemon that should have been KO'd.