I like both in different ways. Rechargeable is really nice and it saves on having to buy batteries. Plus I prefer waterproof toys, and I feel more secure with a rechargeable waterproof toy than with one that has a battery pack.
But if the toy dies on you then you have to wait a bit for it to charge again, whereas a battery-operated toy would simply require a switch-out (though I've never actually played long enough for a toy to die in the middle of everything). Battery toys are also nicer for travel, since you don't need to have the charger with you and even if you forget to bring batteries, it's not hard to find a place that sells them.