not really sure if anyone has compared them to each other...but both shifters have recieved praise from everyone it seems that has them....so you can't really go wrong with either imho....anything is better than stock...i personally have the steeda,and i love it...i also am pretty handy with rigging up stuff and fabricating things to fit...
if you are pretty well mechanically inclined,and can fabricate things then i say go with the steeda,if not just get the b&m and don't worry about which is better...get the one that's better for you...as they are both quality pieces...