I've used 3 other WordPress eCommerce plugins and have even hand coded some PayPal carts into sites (because I hated working with the complex and error prone, limited, alternatives)... ...then someone recommended WooThemes' WooCommerce.
I have built 5 eCommerce sites this year alone and we're still in August. More importantly, I did it with ease, my clients are extremely happy, and their sales have all increased.
Lately, support has been a little slow, but my understanding is that they've grown in popularity and are regularly flooded with help requests.
If you need an eCommerce solution, try WooCommerce first.