Other than being responsive, there are two most important qualities of a well-designed WordPress theme:
page speed performance, and reliable support behind it.
mythemeshop scores both.
the themes rate the fastest ( A & B ) on site speed-test tools such as GTmetrix. I've looked through many themes and found no other that would come near. Not even the themes created by WordPress.org, such as TwentyThirteeen and TwentyFifteen, rate nearly as well.
I've discovered these guys by googling "fastest loading wordpress theme" and read through blogs and forums many of wich pointed to https://mythemeshop.com/themes/apptheme/.
I don't know how they get it to work this fast, however, I am very happy with their product and service, and the price is right.
Test it out and see for yourself.