I have a 2nd-level paladin, with a 17 strength and a 17 charisma. He plans on bumping charisma to 18 at 4th-level, and taking Divine Might asap. He'll probably bump strength at 8th-level, though that's a ways off.

He currently has Power Attack and Mounted Combat as feats.
Here's my query: I'm currently using a longsword and large shield, but I'm strongly considering switching to a greatsword. I'd lose the -2 AC from the shield, but gain +1 damage (from 1/2 again strength) and 2d6 instead of 1d8 damage. Plus I'd be able to trade -1 to hit for +2 to damage via Power Attack.
Is this a good tradeoff? Are there factors I'm not considering? What would you choose?