Shaded Pole is really the best choice from a reliability standpoint for this kind of application. If you are concerned for the fan motor efficiency and don't want to use Shaded Pole, then the next logical step would be Permanent Split Capacitor (PSC). The issue is that when a motor is in the air stream, any kind of centrifugal starting switch arrangement, as found in Capacitor Start or Split Phase motors, will eventually become contaminated and cease to function. PSC has no centrifugal switch.
If absolute efficiency is paramount, then the new paradigm is to use an ECM; Electronically Commutated Motor. this is essentially a permanent magnet AC 3 phase motor that has it's own on-board inverter drive built-in to the end bell. The inverter accepts single phase AC input and converts it to 3 phase PWM to run the PM motor. They are by far the most efficient on the market now, upwards of 97% eff, but are going to cost a LOT more money up front than a Shaded Pole or PSC motor of the same rating. Some OEMs are using them anyway because they MUST get their product to meet certain efficiency standards, so they have no choice. The consumer is who pays the price ultimately though.