See, I want to say Valhalla but for me I find the ride too wet to enjoy. Around half way round I start regretting my decision to board the boat (or swimming pool, as it's usually become by that point).
This sounds like such a cop out (considering my fear of water, it probably is) but my favourite would probably be Congo River Rapids. I love the typical rapid style seating arrangement as it allows riders to interact throughout the ride, I love the 'will we/won't we get wet' factor of the ride. It's a brilliant ride to experience with friends and, on the occasions where I've shared a boat with strangers, I've always ended up being temporarily befriended by said strangers. Let's face it, it's funny when someone takes the KFC mega wave to the face