Mine would have to be Larry "Stay Hot" Bowa. His wit just kills me. I know he had a love/hate relationship as a manager (remember his stint with the Pads) but I could only imagine how he acted in the clubhouse if it's any indication of how he is on MLB Radio.
My second favorite would have to Rob Dibble. The guy really just tells it how it is. I never liked him as a player, mostly because he was on the Reds, but I did see him once at a home game throwing his glove up in the air trying to catch batting practice balls that sailed over his head down the left field line. Strange guy.