I'm picking Nadal, too.
My degree of certainty is closer to 50% than the usual 100%, though. How it inches up closer to 100% depends on the draw. He is a year older, and, except for Rome, really, he did seem to show more signs of his age this spring. And at 34-years-old he will run into the problem that Roger ran into--being consistent through seven best of five matches is a lot to ask. There are more people who can make his life challenging in the early and mid-rounds, and two "next gens" have beat him on clay this year, plus there is Tsitsipas, Thiem and Djokovic, who have also beat him on clay. Though Roland Garros are his equivalent of "home courts," I'm really curious to see that draw.