Try searching the forums - there was a discussion about this a while ago that might have some good info in it for you. You van check out the ratings at
www.mtbr.com . The thudbuster and the Rock-shox style are both liked by many people. The thudbuster, because of its design,
I think means that the distance between your seat and the pedals doesn't change as much as it does when the Rock-Shox (telesoping, like a fork) when it compresses and rebounds. If anyone could clarify this, I would appreciate it. Running a suspension seat post will take the edge of off the sharper bumps, and you can change the elastomers or other material to make the seatpost suspension stiffer or softer. Running lower tire pressure and wider tires are also less expensive ways to take the edge off the sharper impacts. Standing over the rougher stuff (you probably already do this) also helps. Good luck!