I am thinking spies, BHs and Jedi are the most overpowered classes in the game when it comes to PvP....is that right?

I would think stealth from the spy would be a huge asset.

You'll get folks that might say one is more OP'd than the other, but in general, each class is pretty good and decent in PvP.  Some have a few weaknesses, but those can be overcome:

BH: great in pvp mostly as snipers or 1v1, they get slammed in heavy group fighting

Spy: great for taking out single targets and fringe fighters, but otherwise, spies are out of place in heavy group fighting

Smuggler:  ranged smugglers are deadly in pvP.  Well timed AoE spike attacks can turn the tide of a fight.  Close combat witha smug is rsky due to Pistol Whip

Officer:  One of the big players in PvP, due ot massive AoE and group support. Not Op'd though, but they shine best with a smart group

Medic: classic group dependant class, though a medic with the DOOM set can dish out some seious Damage over time hurting

Jedi:  Dark Sided spec'd jedi do very well in PvP. Lightside jedi, not so well.  The tanking system build into the lightside tree doesn't work so well in PvP because a LSJ can not FORCE a target to aggro to him like they can a PvE target.

Commando:  A great PvP tanking machine and decent AoE damager.  Commandos shine in 1v1 or in 1v2 or 3. 

Yeah, with all the buff stacking people can do, every profession can take out another profession fairly well. DOOM Medic is surprisingly dangerous :)