As one that love working with Magento i just wanted to show you this article.
If i were in the works of setting up an site for online commerce, i wouldn't choose ZenCart or OSC. They are both old and doesnt update at all. But thats just an personal opinion. And i work a lot with these things.
My Prestashop knowledge is limited though, but if its anything like Magento i would recommend it. Cuz Magento is by far the leading commerce platform atm. Also just my 2 cents.
Magento vs Prestashop
More reading OSC vs ZenCart
