What's your least favorite version of DND?
I will start by echoing what others have said here. Every version of every game out there is going to be someone's favourite and someone else's least favourite. And everyone is going to have a favourite and least favourite genre/setting/rule system/gaming philosophy.
Personally, the very first RPG I ever played was D&D (the 1983 Red Box). Started buying the AD&D hardcovers with my Christmas and birthday money pretty soon after that. As a teen, I loved it, and it literally changed my life (no joke), but even then I saw its limitations. I've either owned or read the rules of every edition since, but rarely if ever played. What I realized was that the part of gaming that I loved the most was storytelling and D&D is almost exclusively a combat rules system. Almost everything is geared towards winning combat encounters and being rewarded for it.
To illustrate: the last time I DMed a game of D&D (3.5 I think), one of my players was a paladin. In every battle, he would chase down fleeing enemies and cut them down. Once the encounter was over and I asked, "What do you do now?" he would be the first to pipe up: "I roll the bodies." Because of course he would. The only way he gets rewarded with XP is by killing enemies, and the only way he gets loot is if he grabs it off the bloody corpses of the enemies he just slaughtered. Role-playing a lawful good holy warrior be damned.
Now of course I'm exaggerating for effect here, but not by much.
I've found a lot of RPGs fall into this category. It just isn't my thing, but I will never criticize anyone who enjoys this kind of play. The thrill of a good combat encounter is awesome, and D&D has offered this for decades with varying levels of crunch. But me, I want the fluff, so I look elsewhere.
So to summarize: I guess my least favourite version is..all of them? With maybe the original basic ruleset having a special place in my heart for its positive and long-lasting effect on my life (but I wouldn't ever play it again).
Again: no disrespect to anyone who loves D&D, or any other game system, for that matter. De gustibus non disputandum est.