If it comes down to looks it's probably not the toy I really want. I love the look of the ufo but it's ability to perform and lack thereof keep me from getting it. But I do consider looks somewhat. I'm planning on getting the eroscillator even though it's ugly as sin because it's so highly rated.
Functionality usually comes first and aesthetics, second. First off, I want a toy that works; a pretty toy that doesn't do its job isn't worth it. That said, there are usually enough (roughly) functionally similar toys available that it's possible to find one that works well and looks good.
Note, however, that in some toys, functionality and aesthetics are effectively intertwined. If I'm getting a BDSM toy that's primary purpose is to intimidate, the way it looks is crucial to its effectiveness.