1. I want to learn Suiton because it is a very versaitle element when you get good enough at it, which means using Suiton without the water source. It has a good mix of attack, defense, and right off the bat finishers like the vortex jutsu that traps someone in the water without you wasting a hand. Over-all, one of the best elements.
2. Suiton's weakness is Doton. Water flows where it can, not forcing it's way through things that are very dense like Doton. Since Doton is so dense, the Suiton cannot go through it, making the Suiton bounce off (unless of course the Suiton is 1 rank above).
3. Suiton is strongest against Katon. When the Suiton hits the Katon, this causes a reaction to where the Suiton starts to drown out the Katons oxygen, making the Katon considerably weaker or just nullifying it directly.
4. Lord Tobirama, Kisame Hogashaki, Zabuza Momochi, Mei, Hashirama (if you count that), and Itachi Uchiha.
5. Two KKG that have Suiton mixed in with another element are Boil Release and Ice Release. Two KKG users that use Suiton in their KKG are Haku and Mei.