I've been a Joomla user since Mambo days (yes, I'm that *OLD*, LOL!) ... and it takes a fair bit to prompt a review from me.
I've tried all sorts of Joomla carts over the years and they've usually been nigh-on impossible to set up or lack the just that one basic feature you really need.
J2Store (Basic/free) installed in Joomla3 quickly and painlessly - and a simple online shop was up and running in a matter of minutes (honest!). "There must be a catch" , I thought, but no - all the common features are there.
Within a day, I'd persuaded my client to shell out for the Pro version (incredibly cheap for what you're getting).
Inevitably, a few hours later I acquired a "wish-list" or noticed a few minor issues. Ramesh responded *instantly* (and helpfully) in the forum. I didn't even need to raise a ticket. With support like that, this extension/application is definitely "going places".
So ... if you're considering a Joomla shopping cart, try the basic version. It won't take you long to evaluate it - and you'll be a "convert".