This....
http://www.vikingtactics.com/slings_wide.htmlIt'll adjust quickly so if you want to suck it up tight against you to keep it out of the way, it'll also let out quickly so you can shoot. Kinda handy.
I've found that I like the padded version, because I'm a sissy. And it seems to stay in place better, especially on a stiff surface like body armor.