The Gripster pads are nice, easy to cut out, and contour to the sides of the tank really well. BUT, don't spill any fuel near them because they easily delaminate from their backing and end up looking like *****. On the plus side, they aren't killer on the insides of your thighs and knees like the Stomp Pads are. However, the Stomp Pads seem to hold up to abuse better.
If I had to choose, I'd go with the Gripster pads because they're lower profile, don't kill your legs in jeans, don't look like shower mats (where are the black Stomp Pads I saw in a magazine?!?), and if they get crappy they're easy enough to replace.