Druid vs Wizard - which is the more powerful class?

Druids by a mile. Sure, wizard spells are better, but the first goal of D&D characters is to not die, and hit points and fort saves are always useful. Also, druids have skills and modestly effective combat options when their spells run out or aren't useful, and druid pets are better than wizard pets.

Conversely, wizards are all smoke and mirrors. Your power is predicated on tricks. To be fair, they're really good tricks and you get a lot of them, but if you don't have the right spell available, you're a glorified commoner. Sure, you'll get Wish eventually, but for most of your career you'll just be wishing you had it.