If you want the MOST freedom to design your page, I wouldn't use either, but would continue to use BV and then would add a shopping cart - look at my sites in my signature - Pinata Palace and A Child's Palace are both built and designed in BV, and I use CartManager for a shopping cart (
www.moxie-enter-prises.com/cartmanager.html)
If you want my opinion on OsCommerce and Soho, I'd go with Soho if those were my only two choices. OsCommerce has a much higher learning curve. In any of the shopping carts like OsCommerce and Soho, you'll have less design control, as the cart, to a certain extent, designs the pages within the chosen templates. As to templates, both have many, many templates, but I usually can pick out an OsCommerce store at a glance - can't always with Soho, as the templates vary more (IMO).