AIO kits generally aren't better than "big air" tower coolers for temps/noise. However, some of these giant coolers are going to be heavy, and put considerable strain/flex on the motherboard. The AIO kits also don't use the best quality of components either. When you get into custom(depending on budget), things get much better in favor of watercooling. You can have much lower noise than aircooling, much better temps especially for GPUs. Also, after a certain point for OCing, air cooling just can't keep up w/ higher voltages. Besides these reasons, people(including myself)just like to have their PCs watercooled.