Let's admit this is a bit of a dated debate, what with none of the three EPL center-backs in question—John Terry, Nemanja Vidic and Vincent Kompany—anywhere close to the players they were in the past.
If the question is who of these three is the best Premier League defender, the answer depends on how far back we go.
Terry has been one of the great defenders in the history of the Premier League, but his play over the last few years—because of injuries and, shall we say, other matters—has been less than stellar for Chelsea. At times, he has been a liability on the field for his team. Certainly, if we are looking for the best center-back now, it cannot be Terry.
It should be Vidic, who has been one of the great center-backs in the world while in his prime and certainly one of the best players in Manchester United history...when he is healthy. Vidic has been unable to stay on the field for United, though, so it is hard to choose him as the best of the group as well. When he plays, there aren't too many players better than him. When he plays...
That leaves Kompany, and if this debate were had last year, he would be the clear winner after leading Manchester City to the EPL crown. But like Terry and Vidic, Kompany has been battling injuries as well, far less reliable on the back line for City than he was in their championship season.
If I had to pick one of these three, moving forward, I would go with Kompany, if for no other reason than I'm not sure Vidic—probably the better player—will ever be back at full strength for an entire season in his prime again.
That said, there are a host of other center-backs I would rather have before any of these three—Jan Vertonghen, Phil Jagielka, any of three center-backs at Arsenal and probably Liverpool as well. Heck, Kompany is the only one of the three who is even one of the best two center-back options on his own team right now—again, making him the best of the three, but not the best in the league.