Inous
Newbie
Either, as long as the chin is above the bar.
The overhand works the muscles in your back. Improvement is slower, but you have a greater upper limit using your back muscles.
Underhand uses your chest more. Improvement happens rapidly, but it tops out at a lower point.
I started with underhand, while practicing overhand. When I maxed out overhand, I switched for my PFT, because it took less energy overall.
Yea I find that underhand uses more of Biceps and like you said the overhand uses mostly Lats. You'll also find that there are a ton people that are completely in shape but can't do more then 6 overhand pull ups. So if you're trying to do more then 10 overhand pull ups you're in for some serious training for a few months to get over 20 pulls up. In fact out here at our squadron we have a 20 pull up club, and if you achieve the 20 overhand pull ups you get your name on the wall. So far we only have about a 2 dozen.
That's why I was curious as to which, but either way its tough!