I voted for Exploration > Social > Combat, and here's why:
To me, combat is hollow without the stakes built through social or exploration. If all I'm doing is fighting goblins, but I'm not doing it to save a town (social) or find treasure (exploration), then I might as well be playing a board game. Now I really enjoy combat, but again without story stakes (yum!) it's just not as fun to me.
Exploration is the top dog because I love both running and playing it. Unlocking doors, listening for monsters, scouting ahead, avoiding traps, sneaking, solving puzzles, making maps, making plans, making camp... All that just really describes D&D to me. I don't think overland travel is the most important part of exploration, the dungeon stuff is!
Then in the middle is social, because it's fun to pretend to be someone else and interact with the world!