Both are 7-0 in the UFC JDS best wins are Carwin UD Nelson UD Werdum KO1 Gonzaga KO1 I didn't include Cro Cop because he is a Cro Bum he sucks dicks and is always has been overrated. Cain's best wins are Big Nog KO1 Lesnar KO1 Kongo UD Rothwell KO2 I vote for JDS easily. Cain's resume is very average actually. He struggled with the very very average Kongo. He beat Lesnar impresivelly but Lesnar is utter garbage and Big Nog is his best win. Big Nog showed recently he can still go but don't get it twisted he still is very past it and chinny nowadays. JDS has been destrying bitches but then lately went to the decision in fights he should have finished. I think his lack of variety in his offence is catching up to him.
I'd go with JDS too but only slightly. His inability to finish Nelson and Carwin kind of hurts him overall.