Well what kinds of exercises were you planing to do with those weight? Pull ups should be done regardless, doing them as chin-ups, palms facing you will hit your biceps more. Doing both would be better .
Pull-ups are a classic exercise for the entire back, dorsalis major in particular. But if you choose to do them with your palms facing you then your biceps will do most of the work. The best way to do pull-ups for your back is with the pack of your palms facing you while having as wide a grip as possible (wider than between your shoulders, preferably).