I believe Parker is fresher and more powerful, and he would stop him without a problem; Ruiz is finished...
I'm not really sure where Parker is going to be at in his next fight. His performance vs Wardley was "bizarre" and the post fight findings kind of made that make sense... So he's been out for a year, been in loads of wars, who knows what he's got left.
Honestly, right now I think it would be as close as the first fight. Parker is packing on too much mass, while Ruiz is getting lighter, and his feet, while still horrible, are steadily improving because of it. It would be an interesting fight. I would still pick Parker to win, though.
Ruiz was always limited, but at least he had something of a physical prime. Now he is plodding, limited in his approach, and on the wrong side of 30.