For the Wiggins discussion a few pages ago, I heard that he actually isn't all that great a defender. He has the physical tools to excel, but his understanding of play sets and position is still developing.
But then again, the last time I read about Wiggins, pundits were talking about how he was regularly being assigned to guard the opposing team's best wing player.
Edit: I'm also not entirely sold on Wiggins, even though I'm Canadian.

His jumper still looks kind of weird, his handles are still weak, and his only (albeit lethal) offensive move is his spin. I see his ceiling as T-Mac, but I hope he can do sustain that for a longer period of time than |Mac.