This is the only shopping cart migration tool on the market that I would use. I have been using it for 5 years and the product is spectacular. Takes the hard work out of changing shopping carts and migrating all of your data. Their customer service is sublime also. I have been helped every step of the way whenever I have had a questions and they were even available on weekends (because lets face it, that is when most of us find the time to do this type of complex work).
Cannot speak highly enough of Cart2Cart!!!