Well it all depend's on the system you are going to build overclocking, etc. Using a Corsair H50 atm with two non-standard fan's push/pull config work's very well, the main thing about it, it does not block of a ram slot. Not like some Air Cooler's plus it weigh's very little, some Air Coolers can weigh upto 800gram's plus and there is also the height to consider 160mm plus fitting it in your case.
I'm also looking into custom water, but the main thing that puts me off, is that every so often you have to clean your system out. But l don't think its as bad as it use to be with the pre-prepared fluid's you can buy, maybe one of the forum member's who is ginned up on water cooling can advice.