Fans with three or four blades move more air than five or six blade
fans. They are harder to balance than the five or six blade fans
though.


I completely disagree. I would never buy a four blade fan. Five
blade fans move MUCH more air. I've replaced all the 4 blade fans in
my house with 5 blade fans and the results are much better.

Go for the biggest diameter you can, too. Makes a difference.