Ask at http://www.coasterforce.com/forums/ which is the UK equiv of this site.
Myself between alton and thorpe.
As Chessington and thorpe are owned by the same group, the faster rides that could move have move to thorpe so making Chessington the family park, and thorpe for the teenagers.
Thorpe has saw, stealth, Colossus (ouch my neck ), Nemesis, rush (large power swing ) etc which are all good if you are used to Oz only coasters.
Alton has rita if you like speed, air for a different ride, Olbivion (still good) .
Both have the flat rides etc, but I like speed over something that makes me feel sick.