1. A liquid cooler warranty covers the liquid cooler. Not the components that are damaged if it leaks. So in the case of a leak, your warranty comment is moot.
2. It's been proven time and time again using decibel meters and other measuring devices, that in almost all cases, a liquid cooled system is louder due to the simple fact that more case cooling is required to extract the heat added inside the case from the radiator as well as the fact that with liquid cooling you no longer get residual cooling of other internal components that would normally occur due to the presence of the fans on the CPU cooler in an air cooled system. VRM components, northbridge, RAM, drives, all benefit from the movement of air caused by a traditional or aftermarket CPU air cooler.
The CPU may receive better direct cooling with a liquid cooler, but without water blocks on everything else, in a custom loop configuration, something is going to suffer. Very good, significant case cooling through the use of additional case fans can mitigate this, but again, at the expense of a louder system.
3. Plus, it's an unarguable fact that air moving through a radiator, a radiator that is directly against an external opening in the case, thus not dampening sound at all, makes far more noise due to the resistance of the radiator fins against the airflow, than the noise caused by a tower cooler's fan that is situated near the center of the case and somewhat sheltered from external openings. Radiator fans are more discernable than tower or stock cooler fans, pretty much period.
4. Liquid cooling, degree for degree, is more expensive than an air cooler. AND, in most cases the fans that come with them are not the highest quality nor do they have the greatest static pressure or bearing designs, so most people end up replacing the included fans which further increases the costs. Most air coolers over forty dollars already come with pretty good, to great, fans.
Aesthetics or extremely high overclocks, requiring custom loops, or very small, or oddball, case configurations that don't support large air coolers are the only reasons to use liquid cooling in my opinion. If noise levels are an issue for you I would certainly not recommend choosing water over air.
Also, if your liquid cooler fails for whatever reason. Pump dies, fan quits, whatever, you stand far more chance of catastrophic hardware failures from overheating than you do with a large air cooler. Most tower cooler heatsinks have the capability to dissipate enough heat even without a functional fan to allow for some minimal operation of the system without terrible damage. The small heatsink block on liquid coolers will do little if there is a failure.
Don't get me wrong, water cooling is great, but not for every system and there are specific instances where it should be applied, and those where it makes little sense. Water cooling enthusiasts will of course disagree with all of this, but enthusiasts almost always disagree with anything that doesn't comply with their enthusiasm for whatever the subject matter is.