Not overall but two specific rules.
1. Multiclassing. 1E was more generous in regards to MC clerics and perhaps weapon specialization.
2. Magic resistance flat number eg 50% vs +/-5% per level under/over level 11.
1) 1E. I think this needs clarifying though. BASE 1E wasn't so much generous
in general in regards to MC clerics (denying cleric as a class to most non-human PC's!), however it was
inexplicably generous in regards to HALF ELF multi-class clerics where HALF of their MC combinations are cleric-something. Unearthed Arcana, on the other hand, was entirely OPTIONAL and in many ways gave away the store with regard to single-class access, multi-class options, and level limits. There's not a lot of readily apparent reasoning for either approach. I have pretty much ALWAYS treated multi-classing limitations as being strictly the purview of each individual DM for purposes of individualizing THEIR personal campaign settings.
2) 1E, and the MM-defined +/-5%/level over/under 11th. Not that it matters much as MR creatures are typically quite few and far between and I never saw any reason to change it.
1E has the better aescthetics, 2E better mechanics/layout.
I think people really don't appreciate how much 2E actually did change combat. In dropping many of the 1E mechanics I don't think even the 2E
designers appreciated how they were changing those dynamics either. For example - the repeating 20's on the attack matrices gave even 1st level 1E combatants
who had no bonuses the ability to continue to hit AC's WELL into the negatives that they otherwise would never be able to hit. That's chronically overlooked in significance. PC's then LOST that capability when 2E went to straight, uninterrupted, regular-progression ThAC0. That was compensated for
somewhat when the monsters had HD significantly increased which gave them back some of the inflated ThAC0 they would need (a phenomenon most easily seen with giants and dragons) to hit PC's whose negative AC's now gave them SIGNIFICANTLY greater protection from a wide range of monsters.
Certainly 1E rules, especially combat mechanics,
were just way more complicated, fiddley, even incomprehensible than they needed to be. It's interesting, though, that it was Gygax himself who DISLIKED all that extra complication and never used it in his own games, yet included it in the AD&D rules at the request of others. For 2E (which no longer had ANY input from Gygax), its
default combat rules didn't clean up those poorly written and organized rules, but actually dropped
all of it entirely and used a default actually closer to OD&D, with additional rules like 1E's then all being OPTIONS, yet not then well-implemented to work the same way as they did in 1E (or just work better), given the other combat rule changes it made.
For example, weapon-vs.-AC adjustments. In 1E it could at least be argued that whether the adjustments themselves were realistically representative or not, they were at least individualized to EACH combination of specific weapon and type of armor, whereas 2E (I suppose in an attempt to just simplify it so as to not require a full-page chart of
optional fiddley bonuses) said that ALL slashing weapons, regardless of size, weight, length, etc. should have the same bonuses/penalties against a given type of armor. Piercing and bludgeoning weapons were similarly all categorized as ONE common set of adjustments and not individual to each weapon, making choice of weapon to use a key decision that changed with the actual armor worn by an opponent - often superseding the bonus to-hit from magical weapons. This
eviscerated the whole purpose that 1E had in providing that big chart in the first place, for all weapons and armor class combinations
individually. 2E designers seemed not to understand at all what that table was trying to do (even if it did it badly). Rather than make it work BETTER as an optional rule in accomplishing that original goal, they seemingly said, "It's
simpler than 1E's full-page table and therefore
empirically and uncontestably better for... whatever it is it's doing." I mean, I never personally liked WvAC and tried it and discarded it in both editions, but 2E's rule was
awful compared to 1E's.
So, I think there are subtleties to 2E's changes that DO NOT make it
automatically better than 1E's admittedly awfully organized and often clumsy mechanics. I love a lot of things that 2E did differently than 1E, especially the incredible potential of kits (when kept in check by the DM for customization of
their setting, as opposed to all being free and open power-ups for players to use), but 2E also threw some babies out with the bathwater just because the bathwater itself was obviously dirty.