I have used both. They are pretty much identical - but I prefer GAF. Why? The price is a little cheaper, but the shingle is very hardy. I use a GAF system - GAF Shingle, GAF Deck Armor, GAF Ice and Water Shield, and GAF Cobra Ridgevents. If you call or check the GAF website you can find a GAF Certified Contractor in your area. By using him, you will get an ironclad guarantee for your roof up to 55 years. I don't know of a comparable program with Certainteed.