Hackmaster picks you!I have to say, I’m slightly surprised nobody has picked Hackmaster.
Hackmaster picks you!
Choice 1: 3.5e, with adventures and materials imported from Basic, AD&D, 2e, 3e, PF1, and 5e. It’s what I already do, and it’s designed to be able to absorb older sensibilities and of course PF1 is just a branch.
Specifically, I mean only PHB, DMG, LGG, and Monster books. Everything else is banned unless I decide to admit it. That means I have around a half dozen extra feats, 1 extra prestige class, 1 homebrew class variant, all from Splatbook, Unesrthed Arcana, modified PF1, etc.
... that ACTUAL AD&D 1e is still available (via POD even). So I picked up the three core books, UA, Dungeons of Doom, and Temple of Elemental Evil. I'll look at some of the other suggestions in this thread as well. Thanks, folks!

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.