Valero completely unproven at 140. I'd say Mathysse sparks him. 27-0, 27 KO's baby, there is no blueprint.
Matthysse is more proven so I'd say him, but it's nigh on impossible to be sure just how good Valero actually was. All I can say with certainty is that it's a fight I would absolutely loved to have seen
I'd go with Lucas. Valero tended to be very wild at times and would leave himself open. He always got away with it but he never had anyone as good or as heavy-handed taking advantage of his mistakes. Valero would leave his hands low and lean away from punches at times - I think that would've cost him against an accurate power-puncher like Matthysse. It would have been ridiculous to watch though, whatever happened.
Valero is more accomplished of the two, but he is completely unproven at 140. Honestly I wouldn't know what to tell you.
Valero's last fight was a masterpiece, after all the gym stories how he owned Pacquiao to Mosley to Oscar in sparring, it was the evidence that he possesses some real skills. What a tragedy on personal and professional level. He was the real deal IMO.
Matthysse clearly has more power imo, Valero was more of a volume puncher. Valero was more than just a banger but he pulled away with his chin in the air at times, and with the amount of punches he threw, he would have got caught and finished by Lucas.