My favourites are the scenic adventure type, since I'm a sucker for theming. The ones that also incorporate a decent drop or two are the best. I'm thinking specifically here of Jurassic Park and Splash Mountain, which are both absolutely fantastic rides.
I enjoy Shoot the Chutes, too. The drops on those can rival a lot of coaster drops in my opinion. My favourites are the models at the Happy Valley parks: huge drops combined with great theming.
Log Flumes. Very hit and miss for me, again often depending on the theming. A pet peeve of mine is slow log flumes that scrape and bump along the trough. I hate that feeling. If they're fast flowing, and have a decent drop and/or theming, I love them. Best I can think of off the top of my head would be at Space World (weird, twisting drop, big final drop and cool theming), Yokohama Cosmoworld (best log flume drop ever), and Formosan Aborginal Culture Village (fast flowing with great theming).
Rapids. Hmmmm. With the right people, they can be a lot of fun, but as rides there are a lot of really crap ones. There are a few that I really enjoy, though, and I'll always give them a go when I'm at parks that have them. My favourite is probably at Lotte World. It's short and not wet at all, but it's very fast, themed fantastically, and the fact that it's all indoors, almost hiddden near the top of a seven-floor building blows my mind. The ones with the "bendy" boats (Vekoma I think?) are also very good, due to how low they sit in the water and the amount of water they let in.
Splash Battles? Meh, and still yet to try a water coaster.