I think my favourite would be my first D&D which was the Mentzer Red Box. I loved the simplicity of the design, the feel of the world, and the artwork. But I wonder in some way if I like it more because, of all the versions I've played, it's the version I've played the least. I quickly moved on to 1st edition AD&D, completely buying into the hype at the time that it was the one true path. I then dropped out of the game entirely for many years. I dipped back in with some 2nd edition AD&D years later, but I didn't get inspired again until the release of 4th edition. The only real problem I had with 4th edition was getting my group back together. The editions had totally split my old gaming group into the 2nd edition die hards, 3rd edition die hards, and those who were bored and wanted something new. But it was 4th that eventually broke the deadlock and since then we've played 2nd, 3rd, 4th, and 5th editions. 5th edition eventually won out, I think because it's everyone's second favourite.

The argument that B/X and BECMI being "bad game design" is a purely retrospective view. At the time it made a lot of sense, and my first D&D game ever was run by my junior high buddy was using the Mentzer Red Box. I saved up to buy my own soon after, and taught myself to run games from the DM's book. There was pretty much zero way you were going to teach yourself to DM using AD&D unless you had some prior experience in either playing D&D or possibly double-blind wargaming. As a 12 year old kid, the Red Box served its purpose: to introduce more people into the game.

You might call it "bad game design," but it was ingenious for the time.

Warhammer Fantasy RP 1e