It's been a while since I've seen both, but I believe there is more room in the vison dome because of the 19 inch grid. With the larger grid, you'll get more working area as you go vertical in the dome. It's beneficial if you want to stack stuff, especially the long meats like ribs. The best cooking space in these cookers (searing excluded) is in the dome, so more the better.
Check the reviews but I think KJoe gets better reviews on build quality for the metal parts - carts, bands and such. On both, it's still a little to early tell about the ceramics as neither has a long enough history in the market.
In picking a ceramic cooker, how easy to get warranty parts is important. Doesn't do much to have something warrantied for life if it cost you a C note to get it shipped to you.