Don't ignore Power Attack. It depends on your build of course, but I completed my Challenging run with a 2-handed fighter, and for those guys, Power Attack is one of the centerpieces of the build.
Regular power attack gives 10 extra damage per attack by the high Stankmaker levels. But if you wielding a 2-hander, you get 1.5 bonus, so that becomes 15 damage. But a 15th level 2-handed fighter gets an ability that doubles that bonus, so 2x bonus, meaning 20 extra damage per attack. Now my build was a crit build naturally (15-20 crit threat roll for elven curve blade), so almost 3rd of the time I was critting on my 5 attacks per round (with Haste). So 3rd of the time, extra 40 damage per attack. That's more than some builds attack damage.
And also, 2-handed fighter has VERY high AB. With fighter BAB, +5 weapon, weapon focus and greater weapon focus, advanced weapon training, gloves of dueling, and then throw in all the bonuses from bard songs, heroism, buffs, etc, my last attack in the round was usually 20 + 20. So in most cases, the -5 penalty from Power Attack didn't change anything. On the other hand, the extra damage helped overcome damage reduction almost every enemy has in the later chapters. Between the Penetrating Strike feats and the extra damage, I was doing ridiculous damage to everything.