I've played OD&D, B/X, 1E, BECMI/Rules Cyclopedia, and 2E over the years.
When they were first out and I was a kid B/X was the starting point and everything else (BECMI, 1E, even 2E splatbooks) was generally used as an add-on to those core rules.
Post 2011 - when I started playing again I've tried most of the options in a more rigorous manner, but have found that my personal game is OD&D (the LBBs, no Greyhawk etc) because I find it excellent for dungeon crawls due to a flatter power curve and the ease (or necessity) of adding house rules. I find OD&D's quick and very dangerous/swingy combat with Dd6 HD/damage dice pushes a greater emphasis onto the exploration part of play.