First person, it's how I played Morrowind (until waaay late in a couple playthroughs when my characters had enchanted fancy clothes on so they was actually worth looking at). I started with Morrowind sooo Oblivion I played in first person too, and thus we land at Skyrim. Switching to third kills the immersion for me, though I have done it on rare occasion as it seems to be easier to see the ground in the dark with the light source spell going (why it's so much crappier in first person is beyond me) and also I've done it to watch the sparklies when absorbing a dragon soul.
It's kinda funny, I always played EverQuest in first person until I got a horse for my cleric (eventually, whatever the heck expansion that was) and yet always played WoW in third person. The camera in third person for EQ was kinda wonky whereas WoW's third person camera almost seemed to be made for it (plus your character is something more to look at) so I guess that's why.