Re: Which type of cheese grows mold fastest?

This is an excellent question.  Two key factors which influence the growth 
of all microbes (bacteria, mold, yeast) are pH and water activity (or 
available water).  Water activity is not the same as water content, but 
they are related.

In keeping with this, high moisture cheeses will generally grow mold 
faster, so very hard cheeses like parmesan will take a long time to mold, 
cheddars will be faster, mozzarella faster still, and ricotta or cottage 
cheese fastest of all.  Now this assumes pH differences between these 
cheeses do not play a role, but in reality they might.

For a related discussion of cheese safety, see my presentation "Say 
Cheese" here: http://www.foodsci.rutgers.edu/schaffner/presentations.htm.  
Note that this is a technical presentation, written for adults, but it 
does give pH and water activity values for many cheeses.  Your parents and 
teachers may be able to help you with understanding the more difficult 
parts.

Other information you will need to think about for your experiments:  

(1) Some mold is toxic - be careful, ask teachers or parents for advice.

(2) Mold can't grow unless it's spore are present, and not every package 
you buy at the store may contain spores.  Will you rely on naturally 
occurring mold or will you add some yourself?

(3) If you add some yourself, where will you get it?  Moldy bread?

(4) If you rely on natural contamination, how will you be sure that all 
your samples have equal contamination?

(5) Some cheese already contains mold... Blue cheese is blue from mold!

(6) Don't forget, some mold is toxic - be careful, ask teachers or parents 
for advice.

Good luck and happy experimenting!