From my point of view, it all depends on how much storage room you have. If storing the larger Q isn't a problem, I'd opt for the larger grill as it gives you more space for grilling if you are cooking for more than 3 or 4. But, if storage room is a concern, the 100 will work fine. I've cooked for 4 on it and not had a problem.
If my larger Weber grill at home ever dies, I'd consider getting the 200 for use at home at while camping as the 200 would be more than adequate for all my grilling needs.