Have you considered OpenCart? i used to use os commerce but I'm not a big fan of the code - lots of tables withing tables etc.... OpenCart is a lot cleaner and the admin system is very easy.
My preference is Zen Cart. It's perfect for my use. However, you have to look at your situation. OS Commerce seems to be updated rarely and it's not so easy to play around with in my eyes. I've not tried cube cart, so i can't comment on that one unfortunately
Just to throw another cart out there, which I like more than OSCommerce, is OSCMax. based on OSCommerce, has alot of preinstalled mods and easy to mod further.
Creloaded or Osc max would be fine.. there are a lot of oscommerce contibutions avaiable for customization and integration.
I think OS commerce is better than others. first it is simple, second it is best. it has more facilities.
OS Commerce good but if you go for a paid one go with x-cart. prestashop is good also but shipping setup sucks on it
Have you had a look at OpenCart. I came across it the other day and it looks pretty good. Mark AMPG IT Services Ltd