Druid doesn't really have much to offer, in my book. For the character you're trying to make, I'd recommend Earth.
Earth offers:
Earthen Strength, a useful buff if you're fighting things in melee - raise spellpower instead of strength, since the bonus ES gives is equal to your spellpower..
Excavate. More loot is good. It's not a huge bonus, but it's a bonus. Careful about being lured into moving too slowly..
Earth Ripple and Portal. Portal is an awesome tool for avoiding fights, creating safe routes through the dungeon, and just getting around. Earth Ripple is also nice, but can be replaced with a pickax, so it's not all that impressive.
Trap Alert. With just a little investment in spellpower (or Arcane Lore, if that's the mastery-to-spellpower talent), this can easily bring your trap detection over 100%. And you get a 50% bonus to evading a trap once you've detected it, so even if you blunder into traps just after detecting one (I do this), you've got good odds of walking away.
Earthquake. Not a very good screen-killer spell, but it's better by far than none. Screen-killers are handy for spellcasters and other monsters you don't dare look in the eye.
Remove Traps. The radius of this is affected by your spellpower. A supremely high (40 to 50, more attainable than you think, with items) spellpower will allow you to destroy all traps on the level with a single spell. That's probably not an option for your current playstyle, of course.. but even so, Remove Traps is a guaranteed method of defeating traps.
Other viable choices for a thief/fighter/mage would include Warlock, Illusion, Star, and conceivably White.
I'll stop there. I could write a couple sentences of notes on every single spell in the game at this point.