Yes, Buu is stronger than Cell. Proof? SSJ2 Gohan couldn't beat Majin Buu, but could beat Cell. If thats not enough for you, Super Buu(Gohan Absorbed), being the strongest buu, could only be defeated by a fusion of Goku and Vegeta. The fusion made them WAY more powerful than Gohan could ever be. So, Cell is weak, and Buu's powerlevel is OVER NINE-THOUSAND!!!