To elaborate, Psion is the best of the two if used in-tandem with other lists due to Synchronicity, Link Power(a feat), and Schism. (If you're feeling especially silly, you can also use Soul Crystal, which is similar to imbue with spell ability but way better, with your familiar for even more actions.) This is largely because the power level difference between the top few spell lists is far less than that which comes from extra spells being cast in a round. To put it another way, having three classes worth of spells is pointless if you can't cast them all.
Of course, if you're playing a Sharn like I suspect, the mass action spam will cause so much confusion that even the most munchkin player would regret bothering. Then again, druid doesn't mesh well with Sharn so Psion is still the best.