Try to stay away from asphalt based tar-mats like FatMat. I have used FatMat before (50 sq. ft.) and it made my car smell horrible. It also melts in moderate temperatures. Dynamat is great, and I have used both the original and Xtreme with not much noticable difference. I would seriously recommend Second Skin. A great brand with amazing service. If you want some customer input, read here about Second Skin:
SSA Car Audio Forum -> Second Skin Audio