UZR has its flaws, but it is light years ahead of any of the traditional defensive stats. As you mentioned in another post, to get a true assessment of a player, you need to look at as many metrics as possible, as well as watch the player play.
That said, if I'm going to choose one defensive stat by which to judge a player, it would be UZR. Personally, I tend to look at both UZR and DRS, and I think that gives me a pretty good idea of how a player has performed defensively.