For me, it's 2e. It's what's most familiar to me. Honestly I think the differences between 1e and 2e are overstated, and the most important differences get overlooked in favor of more emotional reactions. But then I have an extensive 2e library and most of the stuff that wasn't in core 2e is somewhere in the library or I don't miss it.
Demons and devils? Planescape MC or even MC8 (though MC8's XP Values are massively inflated).
Illusionists? They were just a variant MU with a different spell list anyway. 2e does hose them a bit, but the specialists overall weren't a bad idea.
Monks? Scarlet Brotherhood if you want the traditional class instead of a kit or specialty priest, but the traditional monk has always sucked.
Assassin? They were a griefer class and even Gary was considering making them optional. Good riddance. Oh wait, they came right back as a Thief's Handbook kit. Also in Scarlet Brotherhood.
Cavalier? Unnecessary in the first place. Gary's ideas for new classes weren't great IMO, and cavalier was more than just a bit overpowered. Plus, there's nothing it can do that a fighter shouldn't be able to handle. They deserved to get demoted to kit.
Barbarian? Too many problems with this one, particularly their antipathy to magic.
Thief-acrobat? Too over specialized, and NWPs handled its abilities well enough. They were better served as a kit.
Half-orcs? I think they were collateral damage from the assassin, because that's all they were good at. They got a mention in MC1 IIRC, and later the MM. If you absolutely must have them as a PC race, then the Book of Humanoids or Skills and Powers are sufficient, but they're hosed by their level limits. They don't have a niche in 2e.
Rangers? Ok, you got a point there, though I'd argue that the 1e ranger was overpowered and every subsequent edition took turns beating them with the nerf bat. And 2e was one of the editions that got excessive with the beatings.
2e did leave out a lot of little things here and there that tend to be associated with old-school play. I've been examining dungeon crawling, how it worked in the old days and how to tweak 3e to bring it closer to that feel. There's a lot of little things 2e discarded there, and sometimes 3e wrongly gets the blame for it. When I'm done with that, I'm moving on to wilderness adventuring and then domain play. In spite of its flaws, 1e does have elements that are useful for filling in some of 2e's gaps.
Old school thieves were always weak. The biggest problem was the percentile rolls that governed their abilities and often started to low to be very successful. 2e at least allowed some customization. But they were always an example of a class with too narrow a focus that was also too weak.
For the original options, I'd probably normally almost always choose 1e over 2e for those two.
Interestingly enough, in response to some statements in the thread...the 1e versions of the Assassin and Monk were available in a slightly tweaked form in 2e via the Scarlet Brotherhood book.
Also the 1e Ranger was in the Complete Ranger and the 1e Druid in the Complete Druid.
I think the 1e barbarian may have been available in the Complete Barbarian (not positive, would have to go back and look at my copy).
The 1e Cavalier was not available ever as far as I know it from an official 2e source.
However, if you HAD the 1e books and used the grandfather clause, all your 1e stuff could be used in 2e...if you wanted it to be.
The one thing I missed in 2e was Wild Elves/Grugach. They may have made an appearance and I just forgot about it, but my memory kind of tells me they just used Wood Elves from then out instead and erased the Wild Elves from Memory.
Pity as I loved Wild Elves.
The Paladin's, Ranger's, Druid's and Bard's Handbooks all had an appendix that summed up the 1e rules for the classes.
The Barbarian's Handbook I think mostly updated the 1e class with some small differences. Some of the original class's survival abilities and the like though were covered by NWPs in 2e. I'll be honest, I passed up that book BitD because they mostly came off as fantasy Native Americans and I was looking for Conan.
Cavaliers were a kit in both the Fighter's Handbook and Skills and Powers. Like I said, I don't think they ever needed to be a separate class.
Grugach were in MC5. 2e seemed to have tied them in specifically to Greyhawk.