I've done water water.

I wouldn't recommend it even as a ranking option.

Some ranks were stupidly easy. For example, I had ranks where my mobs used drowning attacks to which I was immune, while I had electric attacks (not electric eel) which they were super vuln to.

Generally though it was hard slog and I would recommend against it. The only real point I could see is if you just wanted electric eel to stomp people with at the first possible levels to get it.