Which devices should I target?The purest answer is none of them.More and more devices are going to come to the market and it seems silly that a device with 767px assumes a 480px design because that’s where you set the breakpoint.  Instead if it were set at 800px and again at 600px (or at what ever point the design looked shit) then you cover ANY device that comes along tomorrow, next week, and years into the future.If you do want to target specific devices we’ve still got you covered, check out this list of common device breakpoints for responsive design.

Quelle: Defining Breakpoints | Responsive Web Design