I voted for Tornadoes, when you ride with a fully loaded raft, the amount of height and airtime you gain is just awesome, as is the drop if you end up going backwards. They're great for the group fun factor, and they seem to have a fast moving line which is also a plus.
As for the rest...
Extreme slides are also awesome, a close second more me.
Uphill slides and natural rapids are "OK" but nothing special.
Raft slides and body slides are good for what they are..body slides are fun for the fact you have a bit more control, so you can straighten up, arch the back, and go at an irresponsible speed.
Family raft slides and toilet bowls are about equal and very good rides if you can get a full raft.
As for mat racers....I do have a preference for the octopus racers, as the standard type are a bit bland, but racers have a definite re ride value.