Typically I shy away from packaged flour mixes, because I like to have control over which flavors I am using, and not every mix works best for every situation. That being said, I've had good luck using Bob's Red Mill All Purpose GF mix for pancakes/waffles and as a generic thickener for sauces, etc.

But as far as cake mixes, brownie mixes, bread mixes, etc., I prefer to use my own. For example, I love the flavors of buckwheat and amaranth, which are unlikely to show up in most packaged mixes, and I tend to vary the starch:flour ratio of my GF creations depending on what I am making. It may seem more intimidating trying to assess how to use the many different GF flours out there, but I feel that it gives one more freedom - and more tweaking ability to develop a successful recipe.