1st person can get a pic chaotic at times, and at times it is very hard to maneuver your character.
Also with first person you cant see who is behind you,
I prefer 3rd person, you have a better feel of the character,freedom of movement is more realistic,case in point the The Hitman series. Look how wonderful it feels to roam around in 3rd person blasting people,or sneaking up on them and fuckign them up like an assasin.