ATB doesn't need servicing, and the locking action is apparently more progressive, however from what i've been told if you lose all traction on one wheel (e.g. it's in the air) then you lose drive to the other as well.

regular plate type lsd tends to be a snappier locking action and you will always have grip. from people I know who race, they definitely prefer plate type as long as it's not from quaife due to their shocking after sales service. (apparently Tranx are a good bet) for road use, ATB is probably a better bet i reckon.

hope that helps. (and hope it's actually correct!)