Whatever is cheapest or better yet on sale at Canuk Tire or Home Hardware does it for me. Those can be nice in the corner of a tent or tight grow space and come in all sizes.
Most cheap fans are junk and the expensive ones not a lot better in my experience. I like to keep a spare or two on hand. Always seem to be tearing them apart and cleaning the bushings then lubing with 3-in-1 oil every few months until they finally pack it in.
