MeshMixer has a feature intended to orient the object so that support is minimized. I've tried it and, honestly, I can't make heads or tails out of the result. It's probably cockpit error, but I've never been able to get it to work properly, and I end up doing it by feel so the support blemishes will be out of view as much as possible. It's very likely I'm not doing something right, but I haven't felt a need to dig into it. It's worth checking out. It has a lot more uses than just print orientation. http://www.meshmixer.com/index.html