I've often wondered if Marcelo can be seen as prime Alves' equal on the opposite flank. I surely do consider him a better dribbler and more dangerous on the wing on his own, whereas Alves is best connecting with his man. Marcelo practically owns the LW and drives up from deep to destabilize the hell out of the opposition defense. Carvajal is a more reserved but similar influence on the opposite side. It's why Madrid are able to throw so many men into the box and not lack presence out wide/on the perimeters.
Marcelo had 9 dribbles today. He's so direct and so unpredictable, often running in unmarked and unpressured as well. Marcelo is deeply underestimated by opposition defenses. At most he's tracked back by the winger but there's no way Robben can go that deep to stop Marcelo.
Alves is probably the more clever playmaker of the two. His ability to pick out his man in tight spaces, while looking or not, is uncanny and the chemistry he and Messi had is beyond any other duo in football. I'd also rate him higher defensively if supported well and in his prime. Marcelo can still be burned 1v1 even in the system most advantageous to him and with great support, Robben did it many times today. Alves at his peak was just very confident and relentless with his tackling and surely the better of the two.