I have been doing pull ups for a while,right now I am doing them using 15 lb on my back( I can do 11reps).

I got some mixed messages about what is the right way . Some would say NOT to lower your body all the way down as you will be better off having your muscle contracted,therefore you can get the best out of it.

Others would say to lower your body all the way down.

I can do either but I would like some clarification and explanation about the right way to do them.
Thanks

Vito