I don't know...
I think it would be one of those battles where it would be a stalemate. Both Cell and Kid Buu would be busy trying to acquire many fighters from across the DBZ/GT Universe. It would be just mindless violence and destruction and both would get there asses handed to each other since Goku and Vegetta would have to step in and handle that biz. Besides they both are so weak compared to Truffles or Shinron Omega.
But you don't have to take my word for it.
-Levar Burton and many Kids from Reading Rainbow
Do not fear the night, the sun will come soon.