Willem for me. With water maps, production tends to hit a wall by the industrial stage. My cities just don't have enough shields to build those late stage units and buildings. Being able to put a dike in every city is a huge boost.
I hate the dike orgy right now. Hate it.
Carthage wins this. Like willem, the leader is financial and starts with fishing, making coastal seafood stronger. We get great starting techs as mining is probably the best one, and compliments fishing nicely on water maps (insta BW frequently).
From there, we get a pre-monarchy +2

which goes even further to lift early game research. A semi-early cothon makes trade routes start to look like villages, and gives us an extra one. He just keeps getting stronger.
So now, we're back to which is better: CHA vs CRE and Cothon vs Dike. Cothon and CHA, please. CRE is good for earlier academy, but less useful than normal in water maps because the need for blocking is reduced. The

and warmonger power from CHA is still helpful.
The cothon blows out the dike. There are soooooooooo many ways to get a hold of dike-like production outputs before levees are even available. Let's review:
- Drydocks city with a couple hills or caste/chemistry/guild workshops. Just 1-2 of these cities can easily build your entire navy.
- Drafting
- Upgrading units (note: this makes ragnar very strong. CR II amphibious rifles are absolutely ridiculous and on this kind of map nearly made me pick Ragnar)
- The whip. Biology farms + whipping (with kremlin this roasts even mines and workshops alive) can put out a lot of troops quickly.
- A heroic epic city (which hannibal unlocks more quickly).
Willem (and all of these leaders, and some not listed like roosevelt) are quite strong in archipelago but hannibal is #1. The cothon is really strong...stronger than the dike easily as if you build it in say 8 cities by 500 AD (which is slow) you're looking at 100's and 100's of commerce, if not 1000's. If you want to match the dike output, just put all that through gold multipliers and chain upgrade

, but it's more versatile than that.
Edit: Izzy has a lot of potential for this too...