Due to space limitations (i.e. only inflatable), we went with Zodiac Cadet 3.2 with high-pressure floor and all the other stuff. We're moderately happy with it, but every time we ride, we wish we had space to carry a RIB with us.
Reasons [note that we have an automatic pump
that pumps the dinghy
up to the requried psi, including the floor]:
1. Doesn't track as well, so uses more gas.
2. Doesn't cut through the chop well, so less control and uses more gas.
3. RIBs with 1/2 or 1/3 of our engine
hp easily overtake us in any chop, even with fully inflated floor.
4. Takes more hp to get to plane.
5. When getting close to corals or rocks or when beaching, huuuge anxiety not to pierce that high-pressure floor.
6. Should you leave the boat in the water and barnacles
take hold, they thin out the material. Yes, it's enforced, but still more chance for easier piercing later.
7. High-presure floor or not, once you load up the inflatable with people and groceries, the dinghy
tracks even worse.
Between a RIB and an inflatable [with collapsible alum floor or without], for us it's a no-brainer - only RIB if there's space for it. Smaller RIB is better than bigger inflatable.
To save on weight, as other people suggest, maybe go with a lighter RIB, like alum or Walker Bay, but still a RIB.