It's easily Penn at this point.
Yeah Frankie beat him twice but I personally think Penn won the 1st fight.
Plus BJ dominated the shit out of most of the LW's he fought whereas Frankie rarely finishes his opponents...
He is obviously an off and on type of fighter but, to me, I've never seen a LW that impressed me like the BJ that fought Kenflo and Diego.
Diego is seriously the toughest SOB ever to not have been knocked out in that BJ fight...well technically I think he was knocked out for a second in the 1st round lol...but he somehow recovered...then was still fighting after the brutal headkick and uppercuts in the 5th.