This is the last day for which I know I have a clear answer. The rest may require more thinking…
Favorite Edition of D&D?
I guess it would be the one I started with.
Moldvay Basic / Cook Expert
It was written in just the right way to make it easy for somebody to learn to play D&D on their own, without having to have a more experienced gamer to teach them.
It covers character levels 1 to 14, which takes you from ex-farmboy to land-ruling baron or wizard-lord. Honestly, what % of D&D players ever get beyond that range? I never grew a starting 1st level PC past 6th level or so; just never had a campaign last longer than that.
It gives you enough tools and advice to make your own world of adventures.
All in a pair of 64-page books. (Although having the modules B2 and X1 as examples of a dungeon and a wilderness were a great help also.)
I guess I’d have to toss in Labyrinth Lord as a sort of accessory to B/X, as it is a retroclone of that version. Until WotC wised up and put up PDFs of the rulebooks on RPGNow, that was as close as you could come without having the books from way back.