I have done some major implementations with pretty much all the joomla web shops and have become so frustrated that I was ready to give up on web shops with joomla because of the amount of headache.
I then decided to give Mijoshop a try and have been very impressed. It is by far the best web shop I have developed with. Porting opencart is genius because of the opencart extension support. I have been to find every feature i wanted in the open cart extension directory.
Fair warning though not all open cart extensions are 100% compatible (i did my research a knew this ahead of time) however just make a ticket and they will make the needed adjustments to make the extension compatible.
My support experience with Denis has been really great!