I'd probably say a hybrid between SL/romanian DL on box as the number one exercise for me, since I can pretty much load it the most, of all the exercises hitting hamstrings - even more than powersquat.
Second exercise would be GHR and then legcurls. I haven't really got a fourth one.
Why is it, that some of you prefer DB SL over regular SL DL? Are you doing it unilateral?