This has been discussed before so there may be something in the archives. I'd recommend that if you want to get a much broader range of opinions on raft vs cat from lots of experienced rubber pushers, try a group that doesn't consist primarily of kayakers. You may want to check raftzone-dot-com on boater talk, utahrafters-dot-org, or the Grand Canyon Private Boaters Assoc. (GCPBA-dot-org) discussion groups.
Personally I'd recommend a 14' SB raft for a Colorado raft. Big enough for the Grand, small enough for headwaters rivers. If you're talking about extended multi-day trips you may want to consider a 15' boat. A raft will be more versatile for passengers than a cat and you'll be able to haul just as much gear, easier to rig, easier to outfit, less splashing, and other reasons already said...
I'll disagree with Salto on the Superbug. It'll have to ride with a high center of gravity due to the suspended floor. I'd like to hear how it does in big water rigged with a heavy load for multi-day trips.
Good luck shopping,
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse