I have no experience with the Z&G, other than I think they look good. We have a Weber Baby 100 (high lid), but we found that too small for our family of five. So we recently bought the new 2000 (low lid model online thanks to eBays 50% off deal. Haven't used it yet but I can see from the size that it will be more suitable.
The main reason I chose the weber are.
- I read lots of good reviews from caravan people.
- Weber is a trusted brand, have heard their warranty service is good.
- Build quality seems solid and simple.
- Accessories and parts are readily available form dealers and general retailers such as Masters etc.
- There are plenty of accessories available.
- Bayonet style hose readily available and it is also approved for Natural gas. Many BBQ's are not.
Downside would only be they take a little while to get used to as they are not like cooking in a 4 burner bbq with hood. Reading the book helps

.
Edit: By the way if readers are looking at Weber Q's, there are new models for 2014. As an example the old 200 is now a 2000 etc, so knowing that you might be able to do deals on old stock. I cannot see what the difference is. They still have dealer and general stockist models. Dealer models are better equipped.