Aside from aesthetics and extra features, which is a highly personal choice, you should keep in mind that you need at least 1 CFM for every square foot of space in the room. This should give you a better idea of how powerful the fan should be. If your bathroom is square, multiply the width by the length. However, if you have an odd shaped bathroom, you can simply measure the bulk of the space and estimate, or measure it in sections and then add them all together.