I'd say #19 probably wins, seeing as it's pretty hard to place the #20 that got stomped by Piccolo ahead of peak #19 drained Vegeta enough to give #20 a chance against SSJ Vegeta, unless you assume using the Big Bang Attack took a collosal toll on his stamina or that both Vegeta and Piccolo were factoring in the amount of Ki burned by the Super Saiyan form or #20 getting in a lucky grab on Vegeta.
Actually, that said, there's a bit that could still make Drained SSJ Vegeta > Near enough Initial #20 in terms of raw power. Maybe #20 could win. Either way, I think it'd be close.