It depends on several characteristics: how many products you're going to have, are you looking for a casual or professional look and how much time and effort do you plan on putting into the website?
All things being equal, personally I prefer CubeCart. I think the community here is more comprehensive and the administration panel is more intuitive and conforming to e-store admins.
Unusual amount of support for CubeCart. To me, CubeCart seems like a basic shopping cart, while osCommerce leaves it for dead in terms of how powerful it is.
I love about CubeCart s it's so simple and largely very easy to understand. OScommerce is very flexible, both out of the box and with a lot of mod extensions, but for me that's part of its problem. Options = complexity. oscommerce cannot be used on HIGH TRAFFIC sites well it can if you want to pay your host a load of money, next CC more simple, OSC more buggy, mods easier to make,