The most obvious difference is CTMH stamps are acrylic and SU! stamps are wood mounted rubber.
CTMH has a lot to offer the scrapbooker with the my reflection kits and coordinating accessories.
I personally use both, but am a demo for CTMH.
If you are curious about CTMH and would like to try the products yourself you can go to
www.closetomyheart.com and use the consultant locator (the tab is in the upper right hand corner) to find a consultant in your area