Magento is the best in my opinion. It looks the sharpest, it is the easiest to use, and there is no shortage of designs available for it. If you don't like Magento, Zencart has always been a good option. It seems like I see less and less themes for it every year, but it is still going strong.
Depends on how important for you scalability is. If you, in near future, are planning to have tens of thousands of products, with millions of visits every month look no further than Magento. However, for normal shopping cart product, my thinking coincides with Solmak. Go for Prestashop and if you want to keep it on Wordpress, Woocommerce is the way to go!