What is the MOST stable release?

I have 2.8.8 running on one site I am developing. Not too many products at the moment as it only just begun. For the most part it works fine, but there is a major flaw in the cart system.

In 2.8.8 I cannot add products to cart. You can only use Buy Now which is not an option if you want people to buy multiple products.
See video example:
Site is here: http://www.familytreeclothing.ca/sitecms/

I upgraded my original/primary site from 2.8.8 to yesterday hoping this issue would be fixed (it has) but have run into MANY other issues. So I am unwilling to update the 2.8.8 site until I know there is a functional upgrade.

You can see my running issues with the current release here:

So, what is the most stable release?
Or, how can I fix 2.8.8?

Both sites are hosted on Godaddy Shared Hosting and are running the most current version of Wordpress with custom built templates. Marketpress is the only plugin with any issues.