osCommerce hasn't been updated for ages, the tables in the design/skinning it is one big headache. They barely release updates, shame as they were the most widely used platform at one stage. At the end of the day, it really depends what kind of shop you want to start & the options you need. Zencart is better than osCommerce. Magento is amazing - has a lot of options but might be too powerful for the smaller & more simple web shops.