When I need a smooth, accurate part, I go with Stereolithography. If you are going to make silicone molds for polyurethane castings (good for ~20 parts) then this is my preferred technique.
However, sometimes I need a part that will endure higher temperature. This forces me to use SLS (specifically SLS nylon). It's pretty brittle, but handles higher temperatures.
My experience with Stratasys FDM parts has not been too positive, but I haven't tried one of their newer machines. Surface finish from the older machines was poor.
If you still have questions, try using a service bureau. They should be happy to assist you in choosing the right technology for your application.