Messi's dominance in the earlier part of their careers may be largely due to the collective strength of that Barcelona team. He's amazing, but Xavi, Iniesta, and others really helped at their high point. Ronaldo, though older, has been more effective in the last few years than Messi as Real Madrid have surpassed Barcelona from a team success standpoint. Both all time greats. I'm inclined to lean Ronaldo though.