Myself I am going with Certainteed on my house. It has absolutely nothing to do with the weight and/or thickness of the shingles. It has to do with the fact that I install these almost everyday, I have also installed the GAF Timberline. The amount of granules that come out of a GAF bundle wrapper is scary, where the CT have very little to no granule loss.
They both seal up very well.
I prefer CT (mountainridge) ridge cap over any cap GAF offers.
That and the nail strip on a CT Landmark is 4-5 times the size of GAFs chalk line nail line (less chance of improperly placed nails).
Most manufacturers (CT included) use a dark strip of granules along the top of the exposure line to give that shadow effect, whereas GAF puts a lighter strip of granules along the bottom of the exposed part. This to me looks ugly and stands out too much.