I've used the Tama Iron Cobra pedals since I started drumming and have always used the felt heads. They're soft but dense and don't get mis-shaped over long periods. I recently, however, purchased a practice bass drum pad and thought I'd order these along with it, to test out how good the rubber is compared.
As you might imagine, the heads are extremely solid and a lot more dense than the felt ones. If you've ever had problems with the actual heads turning upwards as well, you don't have to worry about this with the newer revisions of them (like these). After trying them out, I was extremely pleased with them. They bounce nicely and don't feel a lot different, but have a nice definite attack on them.