The Fun is a Free-Runner, and the Allstar is a Freestyle boat. If you want a boat that is designed to run rivers AND play, then get the fun. If you want a boat that is designed ONLY for play, then get the Allstar.
Any boat can be taken down any whitewater (think Ed Lucero's recent 'world record' in a freestyle boat), but boats are not designed to do everything great. There is a lot of information in CKS's new 2006 catalog that will steer you in the right direction for a boat purchase.