It's a very difficult choice between Kompany and Silva, they're both the best players in the world in their position.
Kompany is just outstanding, there's isn't a single weakness in his game as a centre back. Physically (when fit) he's a beast, strong as an ox, very quick, very agile and has a great spring for someone of his size. Technically he's brilliant, his tackling is exceptional, his positioning is second to none, his ability to read the game and make interceptions is top class and he's bloody brilliant on the ball. It's his mentality that makes him our greatest ever player though, he's a warrior, he never gives up, never stops fighting and never stops leading and encouraging his team mates, he is the perfect captain.
Special mention to Silva though, he's the most talented player I've ever seen technically and he's the one I'd happily pay to watch until my dying day.