Choosing between Air- or Water-cooled is a matter of preference.  While water-cooled spindle motors are slightly more work to setup the coolant lines, reservoir, and such, they are incredibly quiet compared to the air-cooled option.  Air-cooled spindle motors are a very good choice as a super simple drop-in replacement for an existing palm router setup.

Most people assume that water-cooled spindles need more maintenance but that’s simply not the case.  Once setup, there is little to no maintenance to be done other than the yearly recommended coolant refresh/change.