The only good thing about air cooler is even the fan is spoiled, the cooling tower still can act as a passive cooler.
For AIO, once any component failed, you need to replace the failed component or replace the whole set immediately.
Nightmare for AIO is pump failure or a pipe leak.
What you talk about has all along been the much debated Pros and Cons of Air vs Liquid cooling.
Water:
PRO: Disperses more heat, no RAM or mosfet interference, looks cooler
CON: More failure points, could be not so easy installation for some
Air:
PRO: Less failure points, some are easier to install, some can be a bitch to install thou
CON: Disperses less heat (generally), RAM and mosfet clearance issues
While comparing better liquid coolers for eg. Corsair H100i, it will probably only give you a 1-3 degrees edge over an up market Noctua NH-D14 But as one increase to a higher level of air cooling, one also increases the noise level, weather it is acceptable to an individual, its up to him.
One also shouldnt compare a H60 vs Noctua D14 or a H100i vs a CM 212 Evo. It will take the larger sized radiator CLC water coolers to begin to surpass the performance levels of the high quality air coolers.