Different sodas do work. Mountain Dew does not work, neither does any orange soda I've tried.
I showed it to my niece and nephew this summer, and we found that
Ginger ale works great! Cherry ginger ale will give you a pink fountain. Diet cola works great too. I haven't done enough experiments to see if it really is better than other sodas, but Coke Zero was a pretty high fountain too. 12 mentos seems to be a good amount, however, you still have to get them all in fairly quickly.
Heidi