thedungeondelver
Adventurer
The unified XP chart. If I was going to DM d20 D&D again and was only allowed to change one thing back to 1e, that's what I'd change. I'd put the old XP charts back in effect. I think different classes (professions, whatever) apply what they've learned differently. And how they learn what they learn goes at a different rate.
If we take a page from AD&D and envision a scene where Morley the Mage, Falstaff the Fighter, Clyde the Cleric and Tom the Thief take down a hill giant, we've got: Morley casting a magic missile spell to do damage, while Falstaff wades in with his long sword; meanwhile, Tom the Thief is looking to get around for a backstab, while Clyde casts a cause serious wounds (hey, I never said these were good-aligned adventurers!).
In d20 D&D much the same thing is going on (except there's lots of...uh...epic tumbles and...um...dire cleaving - but I kid! I kid because I love. Anyway...).
In both cases, the hill giant is slain, loot is taken, there is much rejoicing.
But in the former case, each class member (so I'd always envisioned it) applies what they learned about taking down a hill giant differently. Falstaff figured out that a giant's femoral artery isn't in exactly the same place as a human, so stab somewhere else. Morely now knows that giants get no special benefits against magic. Clyde figures out that his god doesn't mind him killing giants in that particular fashion, and Tom groks that a punch dagger to the base of the spine is much the same here as against bugbears or ogres.
So for me, other than "Well it's just more convenient", I don't really see any point in the universal XP table. Like demihuman class/level restrictions to many of you, there's just no logical in game reason for universal XP to me. I mean I suppose I could be slick and adjust the XP I gave out for each class, but it's a lot easier to just use what I already have...