My fave will always be Moldvay/Cook/Marsh, I guess.
But I voted other, as we play 13th Age more than anything else that is "D&D" in recent years-
REASONS
With the 13thAge companion PC rules it has nearly the simplicity of B/X D&D on the character side (which my players prefer)
Caters to my DM style preference which is focused on narrative and per scene/encounter type adventures and play.
Easy encounter/monster prep or creation on the fly
Interesting and fun to run monster/NPC mechanics in super simple self contained stat blocks.
No hassle narrative focused "Skill" system (backgrounds) with simplified DC system.
10 levels. Perfect.
No need for Magic items for PCs to be "balanced" so you can give out more interesting items
One rulebook, everything else is fluff.
Icon system is something I didn't use at first but since have adapted to whatever setting we are playing in. I have come to love it for the twists it adds to gameplay.
No reliance on having certain character classes in the game (i.e, Clerics to heal, Rogues to do thiefy/sneaky stuff).Recoveries and backgrounds handle it effectively.
Damage based on class (which I used in O/BD&D)
"Zones" for combat, and a simple AoO mechanic (intercepts)
Most people love the Escalation Die- but we always forget to use it

It is great tie in to mechanics/events during a scene (if I remember).
Monster/Adventure conversion is easy peasy on the fly.
I'm sure I'm forgetting stuff, but I love it as a DM. Enough "modern sensibility" without a lot of rules depth/mastery needed on either side of the screen or having to constantly reference books for monsters, items, conditions, spells, etc.