I'd suggest you first figure out what your priorities are for the system you're putting together.
Remember the "good, fast, cheap - choose two" saying? It's a lot like that

You should at least decide if you want a very-quiet system (one reason to water cool) and/or a very overclocked system (another reason to water cool). You should also know if you expect to cool just the CPU or more bits that that
and how big a radiator you can stand having (need it to fit inside the case? how much room is in there anyway?). Oh, right - and there's
price...
I'm no expert (just wandering around here myself), but IMHO if you've figured out some of what you
want the folks who
are experts might just have a helpful opinion.