Ok, it is taking me a bit longer to get this started than I thought, but I will continue no matter how many cookies I must eat! I have found that to have a proper comparison of two gluten free products, you must try both side by side. Double batches of cookies is more of a reward than it is work though, so I can't complain too much.
The two mixes gleefully sampled by my myself, my husband, and my parents, are Bob's Red Mill chocolate chip cookie mix, and Pamela's Products chocolate chunk cookie mix. I picked these two, as they seem to be the most readily available (I have found them at both large and small stores, between here and Canada). I will sample other brands, including Betty Crocker, King Arthur, and Glutino, as well as any others I come across, but my waistline could justify only two batches at a time.
Bob's Red Mill:
Gooier
Slightly nutty flavor? A bit hard to describe, but you could pick them out as the GF cookie in a taste test.
Sweeter
Pamela's products:
A bit dry (I made a second batch, and shaved off some bake time, and it mostly solved it)
Cocoa powder in dough!
More of a semi-sweet/dark chocolate
Overall, Bob's won the taste test. It is more like a classic cookie, while Pamela's would appeal more to the dark chocolate fan. Bob's mix was cheaper as well. However, neither batch will last long with my family, and a fresh gallon of milk in the fridge!
The biggest thing with GF cooking that I have found so far though, is DO NOT OVERCOOK IT! GF is generally dry/crumbly anyway, and overcooking will turn it the rest of the way into crumbs. I usually undercook all baking items about 5-15% of the lowest called for bake time.