I can't comment on Volusion as I haven't used it. I would never recommend the prefab carts like Godaddy or Yahoo. You have no control over
SEO, or your database. I currently use oscommerce but am cutting over to zen cart. Just a newer cart and is css based. Zen cart also has some cms sort of features, although I'm just putting the cart in a subdirectory and a cms in the root.
Here is a link for a Volusion review that seems pretty unbiased. One thing though, it is ASP. There are far fewer resources for ASP than PHP. If you are going to be modifying it you may want to consider that.
Review:
Volusion Review, Volusion Shopping Cart Review, All in One Ecommerce Solution Volusion Reviews by Small Business Arena