I always zoom, just a habit, can't get rid of it..
About first and third person. I personally think 1st is easier to shoot. It's more accurate at short range (you don't have the extra heightdifference) and once you get used to it, it's pretty cool.
As you can see in the vid, I pretty much aim straight for the face, where in third person you'd have to aim a bit higher. I guess if you're used to either, it doesn't really matter, but 1st person is how I learned to play the game.
3rd is better for anything else though, no doubt.