Here is my two cents: I lose more often than not with my Imperial toons, and I win more often than not with my Republic toons.
On the Imperial side, I've brought an Operative (Kuriza) and Sorcerer (Furiza) to 50, and on the Republic side, I'm currently leveling a Guardian (Coola), my 9 year old son is leveling a Gunslinger, and my 6 year old son is leveling a Commando. My sons win more often than not as well, and you can guess how unskilled they are. None of us are guildies, so we always solo queue.
Just another data point for the thread.
Wait, you win more on lowbie pubs? My experience is lowbie pubs are worse than 50 imps. My lowbie imps almost never lose, but my lowbie pubs have about a 60% loss ratio.