When you're picking out your mirror, first and foremost consider its overall function. Do you need a full-length mirror to nitpick daily outfits, or do you merely need a small wall mirror for added decoration? The location of the mirror can alter the size as well.
Although most serve a purpose, mirrors are also great decorative elements. You can cluster several round mirrors together to form a piece of art, or use one sunburst mirror as a focal point for your space.