I'd scale with the most common to your organization / project / country / target audience.
I often find mobile inadequate: a cheap android's screen is simply too small for anything useful, and no matter what, the device will be held around arm-length, and it just won't magically scale up: the "window" to the virtual reality inside just doesn't occupy too much space out of the user's view.
But if most of your users have such screen sizes, that's the way to go.
Or, you can play for buy-in: design first for the screen your managers/customers have. Sooner-or-later you'll have to design for the most common screenfactors anyway.
In responsive design, the question is not about how it should look like on one device: the question is how does it scale.
And that's about 2-3 designs at least.