all my sites, either Service or eCommerce are fully responsive
services sites, blogs and single page websites are built on a GetSimple content management system using Flexi theme, my own base development theme. Nothing is premade. My theme is highly configurable, bloat free with very few plugins.
GetSimple CMS's have an easy to use admin area. mine also have a dokuwiki containing helpful documentation for your specific site. I am one of the rare breed of developer who actually documents everything. it's something I really believe in.
eCommerce sites are built on OpenCart using my own base development theme. As with CMS, my theme is highly configurable, bloat free with very few plugins.
all designs are fully responsive and built mobile first. that means they are built for the smallest viewport first expanding to larger viewports as necessary. this keeps the amount of code downloaded to a minimum increasing response time while reducing bandwith cost.