I've been playing a greatsword-wielding 5th level Fighter in a PBEM the past few weeks, my AC is 15 (it's a desert scenario, I wear studded leather) and I've never been hit, because I Power Attack and I kill everything nearby in 1 round. I find Charge + 5 pt PA (for 2d6+17 damage) is good; or Flank + 5 pt PA, or just normal attack at 3 pt PA for 2d6+13. I Cleave & Weapon Spec too of course. In the last fight our party of (I think) 6 PCs faced 12 desert zombies; I killed 9, the other 5 PCs between them killed 3. I think that says it all. 
