Heck, all of them!
Pandaren -- A nice sound set to go with a cool character. Slow down units and set them on fire with superior Alcohol moves.
Sea Witch -- With Mana Shield and frost arrow? I'm very annoyed when I'm pwned by such a cheap hero in Footmen Frenzy. I do like it when I have her, though.
Firelord -- Another cheap stinker. How can you get to him and kill him if you're NOT a Warden? He surrounds himself with bloody Lava Spawn!
Tinker -- Another stinker who's strong. Oh well, at least he's unique. Who doesn't like sending robot armies, sitting in a gigantic tank, tossing lots of rockets in the air, and getting lots and lots of stats boosts?
Beastmaster -- With the exception of his ultimate, he's pretty cool. I like having a few animal friends who can save my tail every once in a while.
Alchemist -- I don't play him much but he's ok. His abilities are strange, but they fit well--what with Acid Bomb and Healing Spray....
Pit Lord -- With the appropriate artifacts in the map, Pit Lord is unstoppable with his cheap cleaving attack. Otherwise, he's pretty neat.
Banshee Ranger -- One of my favorites. Black Arrow slowly and painfully makes you an army along with Charm. The other abilities I don't use or care for as much.