Are we talking in the US or Europe?
I can only speak about the places in the US that I tend to use. I use moddler for my prototypes. Great detail, no clean up issues with support material as most if it is already cleared.
http://www.moddler.com/
If you intend for them at some point to be cast in spin cast molds, I tend to use VisionProto. They are more expensive than moddler though but I had to use them since that is who Iron Wind Metals works with. You won't find it on their quotes, have to use the contact form and ask for high temperature material so it will handle the vulcanization process. There was a little cleanup needed but most of the support material is cleared away.
http://www.visionproto.com/
If you want picture examples of the prints done by them, let me know.