I actually believe that Lisa Trevor would win purely because she's tough and apparently, in some sense, immortal. Now for all of you this might not be a difficult decision and I have the feeling that the majority will side with the Regenerator, but how about Nemesis as a worthy opponent. Just like the Regenerator, Nemesis is persistent, but takes much longer to defeat, seemingly wearing him down with each battle. Now the Regenerator wasn't actually that hard to kill, you just need to know what you're doing, but they put up a hell of a fight!