Play most Bethesda games in third person. Mostly 'cause the body-and-leg-less first person floating-camera-with-floating-arms mode looks bad. Both in animations and general appearance (when looking down, there's a whole lot more to see than floating arms, the ground and footprints. Well, most of the time anyway), which is an immersion breaker. Also, in third person all those smexy armours and weapons come into their full right. As do the animations. Watching an epic fight between an orc berzerker in smexy daedric armour wielding a great-axe on one side, and a pack of frost trolls on the other. . . well, from third person it looks gorgeous, with fluid animations (well, sort of) and all things blending together beautifully. From first person, it's two hands holding a stick with something on the end of it flying in and out of view with some big white furry blobs in front.
That said, whenever picking up items/aiming ranged weapons/moving things/taking a close look/solving puzzles it's first person time.
Also generally prefer first person shooters over third person shooters, mostly because of how the aiming works. Still hate the floating-arm-with-gun thing going on.
Funnily enough, when playing Mount and Blade (any of them) it's always first person. Probably because there's a first person body.