I started with the TT Bigwater SE because at that time I could not get the Swiftech kits here. It was definitely better than stock HSF and also some of the aircoolers at that time since heat pipe coolers were not available then. Right now, most good aircoolers like the Ultra-120 Extreme would probably beat the performance of TT watercoolers. Of course TT has also upgraded their WC kits to use bigger tubing.
My Bigwater SE pump gave up after 9 months

- looks good though

and easy to setup

but you only know the value of reliability when the pump fails and you can't use the PC

Got the pump RMAed but never used it after that. Currently using it on my second rig but with Distilled water and Swiftech Hydrx additive instead of the crap but expensive coolant that TT provides. With the TT original coolant - algae will form in your loop that probably causes the pump to fail prematurely.
I'm using Swiftech Storm V2, MCP655 pump and Thermochill PA120.2 now and performance, reliability and satisfaction are second to none. Used that with a P4 640 oced to 3.9 GHz for 24x7. Can OC to 4.1GHz for benchies. Swiftech Storm is the best for single core CPUs - proven many times over provided it is paired with a good and powerful pump.
Now on multi core CPUs, the best blocks are the D-TEK Fuzion and Swiftech Apogee GT. I have purchased the D-TEK Fuzion but have not installed it yet. On my E6600, I'm running at 3.33GHz 24x7 with idle temp of 36C and load temps of 51C with board temps of 37C and ambient temp of 30-31C (read no aircon). This is with the Storm Waterblock. I bet the D-Tek Fuzion will give me better temps. But am waiting for quad-core before pulling my tubing apart.
Basically - every component plays a part in the WC loop - waterblock, pump, radiator, radiator fans and coolant. You can use the best block with a poor pump and get poor performance. And if you do decide to go the WC path - get a good spacious case.
Most people who gave up water cooling probably went with TT and gave up on WC because the new aircoolers with heatpipes (using WC principles in a way) are great. But with a proper WC setup ... the differences are obvious. And WC looks great when configured properly.
If you're going for a kit - then swiftech will be hard to beat. But if you truly want performance, go for mix and match. More expensive but can't be beat.
My loop hardly needs maintenance and have not even topped up the water in the last 14 months. If you then throw in GPU and chipset cooling - WC makes the best sense.
This post has been edited by aloy237: Jun 29 2007, 11:13 AM