I'd remove AoO's as I find they do nothing for the game. Tends to cause heated discussion at the table as to whether an action should or shouldn't draw an AoO.
Plus it discourages doing anything other than just standing there and attacking- not very exciting.
I personally tinker all over the place for my games. A quick list of things I've done recently to play around with Labyrinth Lord:
1)Moved all casters from Vancian to one of three magic systems: Prayer, Diabolism, and Elementalism, and made it unlimited
1a) Made magic risky, instead of "use as much as you can as fast as you can, then rest," thereby nearly eliminating the 15 minute adventuring day.
2) Gave fighters a couple of abilities to demonstrate that they're absolute masters of combat
3) Differentiated between melee fighters and sharpshooting ranger types, and stuck in a magic-finding fighter to boot
4)Took out the boring theif and added an assassin and a dungeoneer
That's all in the
Aremorican Addendum, by the way. And it's all free, so you can look it over yourself if you want.