Raystation is very physician-friendly; smooth and easy contouring, countless (relatively straightforward) algebra and contour manipulations, fusions are easy to work with, custom scripting available for a variety of contouring functions, and robust and straightforward plan evaluation modules (easily can view DRR, beam set up, DVH, fusions with treatment plans, etc.). Overall probably my favorite to work with (comparing to MIM, Eclipse, Pinnacle, and iPlan), however I am told it is quite expensive and typically not found outside of academics.