How to nicely communicate to my professor that I prefer a different topic/project
Directly and honestly. It's your job to champion your concerns, not your professor's. They might not have realized Y would be a better fit or have some thoughts about X you are not aware of.


  Hey Prof. Awesome,
  
  Do you have a few minutes to talk about the recent projects assignments? I'm much more interested in working with Y because of reasons. I also think it would be more beneficial to my research because reasons. Can I stop by sometime this week to discuss your thoughts on X and whether it would be possible for me to switch to Y?
  
  Thanks,
  
  Kristof Tak