It doesn't have an HD tuner but HD channels are supplied via your infinity connection as are Sky Sports and BT Sports. It is however a rather unstable box prone to reboots and crashes.
The Catch Up Players (except iPlayer which is the same on both platforms) are different. On the Vision Box the content as provided is a "best of" selection as decided by the TV company. They have no adverts.v
Oh the YouView box they aren't supplied by BT. They carry more content BUT they have adverts.
Sky Sports have a deal with a BTVision until 2016 but have so far refused to reach a deal with YouView.
The YouView option also has other players available like Milkshake and NowTV from Sky with the promise of more to come.