Nadal. He has 4 titles (Nole only 3) and a 2-1 H2H lead. On Nole's best surface. That is huge. Imagine a big clay tournament where Djokovic won more titles than Nadal.
Of course Djokovic is the better HC player, but at USO, Nadal is greater. The argument Djokovic was unlucky doesn't make much sense. Yes he lost to Federer 3 times, but you know that every match starts at 0-0? Nadal, called out for being claycourt-specialist, defeated peak Fed at a HC slam and a grass slam to take his first title on that surface. I know Nole did it as well at AO, but losing to Fed is not unlucky. It's just being outplayed. Also, why is it unlucky to lose to Nishikori and Wawrinka or attaing a lineswoman to get yourself DQ'ed? It's not unlucky. Yes, he underachieved at USO, but to use that as a benefit is very suspect. Also, the easy draw myth needs to be dismantled. Djokovic 2018 draw was not any more difficult than Rafa's 2017.