Generally said best in terms of quality, easy of use/manage, community help. Best for SMC.
When it comes to quality, it almost best. But, difficulty in every aspect and little community help, meaning extra cost of management. This might suitable for middle or big company rather than small.
Relatively good quality in general
- Tomato Cart (web site looks under attack of malware)
Well equipped, newly born. New version of osCommerce.
If you use Joomla, this can be a good choice.
If you use Drupal, this will be the choice.