Is traditional 35 mm film better quality than 4k digital?

The new Star Wars film has inspired me to ask this. The best cinema where I live has gone 100% digital with the option of 35 mm as well. The biggest screen has installed a 4K ultra high-definition projector.

I have two questions. Since J. J. Abrams has filmed The Force Awakens in only 35 mm film and 70 mm IMAX film, would they project the movie using the film or convert it to 4K digital? Also, which is better quality?