From what I can tell the Xoom is the "Nexus Tablet". it was the first device to launch with 3.0 and is the device they handed out and GDC to developers and I imagine folks at google IO will get one too.
It is stock Honeycomb and easily rootable/flashable. I am planning on getting the wifi only version when it is released.
At least I think. The new galaxy tab looks nice too. But I really think the Motorola Xoom will get the updates first since it is the unofficial/official dev tablet.