1e- more character classes. I mean, sure, you could play 1e classes in 2e, but 2e classes were usually weaker than a multiclass or anything in the PHB. I remember playing a Scout from Dragon and being way happier than I ever was as a Thief. Also there was just more things you could be in 1e. Unearthed Arcana is all like, oh, so you want to be a Halfling Druid/Thief? Sure, why not?
There's something about 1e's presentation of the game that makes it feel somehow more fantastic to me. Like I'm reading some tomes detailing an incredible, magical world. Too much of 2e is matter of fact, telling you all the secrets. Like, 1e would off-handedly mention something like "The Rain of Colorless Fire". 2e would turn that into a boxed set!
Better adventures. This is going to be somewhat controversial, but I don't care for most 2e adventures for some reason. I'd much rather play Beyond the Crystal Cave or Expedition to the Barrier Peaks than Swamplight or Tales of Enchantment!
2e- higher level limits for demihumans. Whole business was a mistake; should have just given humans a racial xp bonus. Way more options for characters- I couldn't live without my Complete Fighter's Handbook (and some of the other ones are ok too). Mythos Priests- sure, they got entirely out of hand, but it was so much cooler than being a generic Cleric. Tons of exciting settings! Lots of zany gonzo things.
You want to play a Wild Mage who is a living Wand of Wonder? Or a metal cube with robot limbs and tiny wings? Tame. Let's talk after you make a Tiefling using the tables in Complete Planeswalker's. Or an Alaghi or Fremlin out of The Complete Humanoid's Handbook. Or a Ranger who is turning into a living tree!