We had both (12x36 Jet and 14x40 G1067Z), side by side, at the sunapee craft fair. They're basically the same lathe, except that the Griz has the moveable headstock and larger size, and the Jet has the gap in the bed. Oh, the color is different too ;-)
The only annoying thing about the G1067Z is the 1x12 spindle thread. You can get all the accessories for it, but you can't "just move" to someone else's lathe for demos or whatnot.
As for quality, it took two guys to move the Grizzly, but only one to move the Jet. But then, maybe that one guy was just showing off.