Pique, Ramos, Casillas. They're incredibly overrated because they play for good teams and rarely have to do much defending.
i do think he(ramos) is incredibly good. but, you do wonder how he would do for a weaker side. he seems to get caught out quite frequently and doesnt seem to track runners that well. but like you said, this isnt obvious because his team isnt in defending for large parts of games. at the end of the day though, he is very good on the ball (for a defender), is quick, and is very good 1v1, and therefore can play in a high line. which is the requiement for top teams.