Forgetting about motor noise, are all household fans such as window fans and table top fans equally noisey? Is there a type of blade or grating that is quieter than others for the same amount of circulation?
It's more about the blade speed than it is the shape. The blades in common fans are not highly engineered airfoils, so I don't think you'd find one with an especially quiet profile. Though from an engineering perspective, that is possible, I just don't think you can find it in portable household fans. This article describes sources of noise in fans http://www.comairrotron.com/acoustic-noise-causes-rating-systems-and-design-guidelines, and also lists how fans are rated for noise. Perhaps searching on those terms will point you to quieter options.
For a given amount of circulation, choose the largest diameter fan that is acceptable for your purpose, and run it at a lower speed. At lower speeds you should also find any vibration noise minimized, but you can still isolate it from its supports. Such as placing it on a soft rubber mat for a portable fan.