I own both a GGA and the Q1200. I enjoy both, but for different reasons. In stock setup the Q is superior in use, but the GGA is superior from a storage/portability perspective.
The Q seems to hold onto it's heat better because of a better engineered airflow setup, and the cast iron grates really help in that respect. Using foil as a heat shield and a trivet I'm able to keep temps around 250F, and it gets up to 500F+ if left to preheat for 15 minutes or more. It is also heavier and considerably taller than the GGA. I'm still not sure how I feel about the attached tables as they make the q1200 really wide which is a distinct disadvantage from a space conservation aspect. They also feel quite flimsy, but are nice to have for lightweight items.
The GGA has an unbeatable advantage in how it folds up, stows easily, and has a stable carry handle when folded up. Cast iron grates (even cast stainless) can be added to the GGA while still keeping the overall price at roughly half the MSRP for the Q.
The main disadvantage that I perceive with the GGA is it's susceptibility to wind, but there are some workarounds for that too.
Both are very capable grills, but they each seem to serve a slightly different niche. If you'll mainly use it at home where storage isn't much of an issue and only travel with it occasionally, then I'd go with the Q. If you intend on actually doing some camping/travelling on the regular, or if space is tight, then I'd probably go with the GGA.
Added: I should also mention that the lid for the Q is removable with just a couple of pins to make transport easier, and the tables fold into the grill space for storage.