I used to like ascending AC a lot, then someone on these boards pointed out that determining if a hit was scored is (roughly) the same as the D20 formula.
Add/subtract any bonuses/penalties due to your abilities and other modifiers
Add the AC of your target opponent
If the result is equal to or greater than your THAC0, it's a hit.
Now I use descending AC without complaint and convert far less because of it.
I'm still torn where it concerns saves. Fortitude, Reflex, and Will are very simple, encompassing, and fit well onto characters sheets I design. Though I think a certain amount of "flavor" is lost when compared to things like "Dragon Breath."
If I play D20 anymore, I'm actually just playing Microlite 20--which, barring a few minor aspects, I find very OD&D.