Top-5 in the world? Who knows - I don't watch enough football outside the English league and La Liga to rank all the world right backs, but he was excellent at the World Cup (in a team that didn't let in a single goal in the knock out stage), the best in the tournament for me along with Lahm, was a constant outlet on the right, defended well, has the stamina to get up and down all game, and almost all the time when I watch Madrid he does the same things.
Sure, I've seen him have a terrible game some times, and he does lose his concentration, but can't we say that about almost any attacking fullback in the world? I can about Johnson, and Maicon seems lost right now, I'm sure Lahm's been made to look a fool in the league a few times too (just a guess, I hardly ever watch Bundesliga). Of the ones I see regularly, I prefer Alves the most, but I still think Ramos is a very good player. I think it's difficult not to be when you're a certain starter for Real Madrid under loads of different coaches, and have 70+ caps for the current Euro- and World Cup champions.