Problem being that not too many guys can do a full pullup (gripping bar, palms facing out) or a chin up ( gripping bar, palms facing toward you) for reps. Could write volumes about the value of each hand grip. But the best basic grip, sort of like the middle ground, may be the hammer grip, palms facing each other.
For men who find themselves lacking in strength for even one full rep, might suggest negatives (pull/chin ups), where the body is lowered starting from the top position of the bar and slowly extended to the full stretch position at the bottom. The full stretch being very important in this method also. We are much stronger in negative starting positions. Even BB curls, which is greatly overlooked for building strong and full biceps..
Good Luck