I smoke both SG and GH flakes. In my experience, the SG flakes are much smoother and more refined -- the flavors are just more tightly structured or better integrated.
That being said, I actually prefer GH's Best Brown #2 (which has a touch of burley) to SG Best Brown Flake and its cousin FVF. I also like GH's Brown Flake Unscented (which has a touch of dark fired leaf -- and some people find it to be very much scented indeed!).
I enjoy the tangy, zesty flavors that GH VA's have compared to the smoother flavors from SG. I haven't had GH CR Flake, but I bet it's good. It's supposed to be the unscented cousin of Glengarry Flake which is a wonderful, sweet, bright VA flake (with just a touch of sweet flavoring).
Still, I like both FVF and Best Brown Flake and occasionally choose them over a GH blend. If SG VA's are fine French cooking, then GH VA's are more like Tex-Mex -- both are good, but the styles are different.