Someone Somewhere said:
I don't know what sort of motors they're using in AC fans. I'm also not certain why they're larger.
An AC fan would probably be cheaper if you include the cost of a power brick. Maybe DC would be cheaper if you had several.
The main reason for running fans at <100% is noise. Typically, AC fans aren't going to be used in the midst of a large number of people.
"An AC fan would probably be cheaper if you include the cost of a power brick."
Do you mean DC fan? You wouldn't need a power brick for an AC fan.
So I think DC fans would be better because they are cheaper and more common, and many people would already have the parts (like a 12v power supply). And you can change the voltage. And they are probably safer too. Plus the AC fans are more expensive and heavier because they have more copper and other metal materials.
So I have come up with my own answer: DC fan with power adapter.
Also, I believe the AC fans use a shaded pole motor. In this
video, he shows a shaded pole motor with a propellor that looks like it came from an AC fan like we are talking about. Also, I've seen a few videos of an AC axial fan like this starting up and they sound just like a table fan with a shaded pole motor starting up.