Suiton's advantage as nearly unpredictable versatility.
Katon: You're gonna shoot fire at me.
Fuuton: Your gonna shoot slicing wind, or enhance your blade.
Ranton: piercing attacks
Doton: defensive walls...maybee a sandwich jutsu
With Suiton....who knows. Maybe a wall. A prison?! Sometimes a clone. A mist to conceal one's self, or a big ass dragon. With its harder predictability, it makes for a more versatile element in combat. Additionally, the offensive moves, while they don't burn, shock, or test you apart, would cause massive internal damage like internal bleeding.
And finally, drowning or forms of suffocation are good methods.
This is one reason water is probably my favorite....versatility makes for the best shinobi.