I'm torn between 3e and 5e. They each have their pros and cons, and they both SUCK for different (and sometimes overlapping) reasons, just like every edition of D&D. Both are too bloated (overlap), but in different ways. 3e can be way too crunchy sometimes and feat implementation SUCKS, but it has a more "D&D" feel to me, like a modernized version of it that still has vestiges of the old, like Attack Bonuses (replacing THAC0), Saving Throw progression, etc. Classes feel more distinct and there are somewhat more customization options, with Skills and Feats being more central than in 5e, but unfortunately the implementation sucks and they're a pain to work with in retrospect. I would have to revamp both of them if I were to touch 3e again, but I like the idea of them and won't play a game without them.
5e is way more streamlined at its core, but makes up for it by piling up fifty tons of class related bloat on top of that slimmed down core. The upside is that the core is so simple, and a lot of the class bloat is stretched out across levels, making it more simple to just pick up and go (specially as a player). I've been getting the urge to tinker with it, since I've played it recently, but I would probably change less of it than I would for 3e, making it the stronger contender.
With either one, I would probably trim down classes to just a core three or so (Warrior, Specialist and Mystic) given the chance*, then treat all specialized class stuff as either "subclasses" or feats (or a combination of both). I'm not a fan of prestige classes, so I would drop those as well, but I do like the 5e concept of subclasses. I just think that they could have implemented them better by trimming down the core classes, then treating all specialties as subclasses, making things more streamlined and manageable, while retaining a lot of the specialized options.
5e also has some cool options when it comes to handling spells that I'm starting to like better than earlier editions, like the option of using up higher level spell slots to strengthen lower level spells. Having all spells be unaffected by caster level was weird at first, but I like the fact that characters don't have to rely on their level for spells to be effective, which makes multiclassed and secondary casters a more viable alternative. But dedicated casters can still shine by having greater access to higher level spell slots, giving them more options and power.
Unlike many here I can't fathom a world without Feats (or their equivalent in other games), or what issue anyone could possibly have with them, other than crappy implementation. So if anything I would drop Ability Increases as a default and hand out Feats instead, then turn Ability Increases into a feat, and adjust all feats to match a +2 bonus to a score in terms of power.
*I actually started doing this for 3e a while back, along with a skill and feat revamp, but never finished. Though, it's near completion so I could just pick up where I left off if I ever went back to 3e. But I'd probably focus more on 5e for now, since it's the more viable option for finding players or if I want to publish it later on.