For me it's definitely more about how the separate parts come together as a whole. I don't have a particular interest in a penis unless something else catches my attention first. Also, even though I'm currently just plain old heterosexual to all intents and purposes, genitals aren't usually a factor in attraction for me. There is such a vast and random list of things I find attractive, that I don't think it makes any sense. You might think that would mean that I would find lots of people attractive, but I really don't.