Gotta go with the Hanlon's on this.

Also, really, again, Core >> everything else in terms of imbalance. If you banned Core, with the possible exception of the feats (which were generally weak and are often used outside of Core for pre-reqs), you'd probably have a more balanced game. Probably grab the Bard and maybe the Barbarian since they have unique class features and are the closest to balanced (or at least, are once you get other books that help them out). Wu Jen, or even better Psion, replaces Wizard, Favored Soul replaces Cleric, Totemist (probably) replaces Druid, etc etc.