I should probabaly note im in UK and want to keep my BTC I do not intend to change back to fiat.
all shopping carts allow you to do that.
the choice should depend on the size of your business, and on whether you can live with a shopping cart that accepts only bitcoins or not.
if you are a small shop with a small amount of listed products, and you do not need to propose other forms of payments than Bitcoin, then bitcoinevolution is good for you.
if you have a large inventory, and if you want to propose Bitcoin among other payment options, then you might want to go for bitpay, or another cart that can be integrated with existing software.