I cannot comment on your first choice but I have been using J2store on a couple sites I manage since it was first available, I think that was around 2012-2013. It has come a long, long way and I'm certain they have a payment and shipping plugin to match the needs of virtually every user. If not I'm also quite certain they would build what you need on request. Often they will not charge you for custom created plugins/apps IF it is something that would appeal to many other users instead they will release it as an extension after getting it working for you.
The entire system is very easy to use, built upon the native Joomla system so no conflicts as it all works seamlessly. The interface is intuitive, I suggest installing the free version to check it out but upgrade to the Pro version if you keep it.
I have been using Joomla to create sites since the late 1990's and tried a great deal of carts and other extensions. Bar none, J2store has the best support and response you will find anywhere. They continually blow me away with their willingness to help whether you are new to Joomla or not.
Keep in mind I am basing my experience on using the yearly subscription to Pro version which comes with ticket support. I don't believe the free version comes with support although they have a forum for free users. I have lurked there and their responses there are another reason I don't hesitate to recommend them, they rarely ignore free users like many other cart developers do and they are always knowledgeable, polite and respectful in their responses regardless of how ignorant the questions or outrageous the requests (for something free).
The cost for the Pro version is very reasonable and worth every single penny, year after year. Seriously, nobody compares to their support. These people deserve recognition for their quality support!