Don't know the best, but the DEI floor/tunnel shield seems to work okay for my project. Back of seat still gets warm, but not hot, and the fiberglass that runs about 4" above the headers/collector gets to about the same temperature as if the car sat out in the summer sun for a while. The PSA works real well too. Has not softened or come loose, but I did paint the panel prior to applying the barrier.
I used this on my GT40's rear clip to keep heat off the exterior paint. I glued it to the interior fiberglass with the spray on glue. This was done over 10 years ago, more like 15 but I'm not sure how long it's been (old age I guess). I have had no problems with heat damaging the paint or with the material coming loose. Is it the best? I don't know that answer but it works well and has proved durable.