While the CP is really good, if I had to choose between CP and Osborne, then its hop to the Studios. The Osborne Lights are just too amazing, and a trip highlight for most everybody that I know that is able to go during the holidays. We stayed there for over an hour, and should have stayed longer. At EPCOT, visit the countries to see how each country celebrates Christmas, walk around and soak in all the decorations and festivities, and then hop.
The only bad part is that I understand the special tag at the end of Illuminations can be the best fireworks ever. I still would hop to the Studios. What a great problem to have.