I am looking for a solid CMS with good/tested plugins. Specifically one that is optimized for selling digital goods. Any suggestions?
depends on what feature you will need to sell the digital product. like upon purchase : - does user need to get serial keys? - how many times user can download? - how many ip user can download? - is user eligible for updated product download after initial purchase? In my experience, If you need simple store where user just able to download, no fancy stuff then drupal + ubercart can be effective enough otoh if you need more features, Drupal commerce can handle more complex situation than ubercart but again setting drupal is not as easy as setting up wordpress.
The number of times I've seen people trying to use Wordpress for digital goods and you find someone on a forum has figured out how to download it as the security is so poor. Avoid at all costs. Drupal as mentioned above or (I haven't tried it) WHMCS is popular for digital goods, too. Either are much more suitable than Wordpress (by far).
I highly recommend Easy Digital Downloads plugin. Is an e-commerce plugin for selling digital products through WordPress. Is 100% free to use with no license restrictions. And if you want, I can help you.
As @crick3t stated above, you can use WordPress and the plugin called Easy Digital Downloads. This combination is known to work well and is widely used. Yes, WordPress has security issue in some cases but if you take proper precautions then you shouldn't have any issues. There are security issues with pretty much any type of CMS/Site Builder/etc., WordPress gets seen as having these issues more in part because it is more widely used than similar alternatives. WordPress is also a lot easier to use and set up than some of the other choices which is something to take into consideration.