I'm a big Drupal fan which is why Ubercart is the obvious choice for me when it comes to eCommerce. I've made a couple of Ubercart sites and I haven't been massively impressed. Ubercart doesn't seem very powerful. When you need extensive business logic, it can be hard to theme and has JavaScript reliance. Admittedly I've only played with others like Magento and Zencart, but Ubercart doesn't seem to lead in its field the way Drupal does. I'm reluctant to learn a new eCommerce package due to the time required, but the JavaScript reliance alone makes me wonder if I have to.
I'm a Drupal fan - should I use Ubercart or learn a new eCommerce package?
ecommerce;drupal;recommendations
I haven't had to go into it myself, but my understanding is that the Commerce project is what a lot of future effort in this area is going to center on. Regarding your business logic point in particular, Commerce is intended to work similarly to Drupal itself as a framework to build things on(so a lot of functionality comes from further add-on modules) rather than trying to give you an all-in-one solution that necessarily has a bunch of unstated assumptions and limitations built in.