I love them standing, for variety though so my progress doesn't stall, I will do standing dumbells, standing dumbells one arm at a time, standing behind the neck press, and when I do them seated (which is rare) I will use the bar or d-bells, but NO back support.......If you're bodybuilding the back support ordoing them seated won't be such a disadvantage because it works the shoulders adequately......but if you're training for any particular sport, I would say do em standing because the most functional strength developed in the weightroom (strength you can take and carryover into real life activities like blocking, running, tackling, jumping) comes from movements executed where your body is the ONLY thing between the weight and the ground....but if you really want the occasional variety of doing them seated, scrap the back support.