I play with all of heroes actually. But it depends on which function you have. I used to play as a Ganker or Semi-carrier when we played in official leagues.
But my favorites are : Anti-Mage, Lone Druid, Enigma, Beastmaster, Panda (<3 his ult), Invoker, Shadow Fiend, Mirana, Earthshaker <3, Lich, Specter and etc. Too many to name.
IMO Lone Druid is the most imba hero. Icefrog once nerfed it but if you watch Zhou's replays and if you can farm well to buy his key item (Radiance) around minute 13 you will kick any ass. However any hero is powerful, relies on how to play with 'em.
[Edited by Evanscense, 4/7/2012 1:22:29 AM]