Kendo - 12:30 am on May 7, 2013 (gmt 0)
I don't think that there is such a thing as the best "shopping cart" because it really depends on your website, your product type, delivery method, language, currency, taxes etc. In this respect some may be over complicated because they try to include all options. Some are just plain ugly and difficult to theme.
WordPress is a CMS and there are many different brands of CMS available and they all have add-on modules and extensions to cater for shopping carts. There are even some CMS that are essentially a shopping cart like Magento.
Not knowing what your product and vending terms are, no-one else can properly advise you. So try them and spend some time at it because once it's installed and populated with your products, you will be married to it.