Resolution itself is not that important. Ratio is important. If you build a game you want it to look well on ALL possible devices. So you have to do it responsive. I use Scale Outer with screenAdjuster/safeZone and use ViewPort's to set objects on the border of the screen. It fits perfectly any mobile device.
The same goes for desktop apps. My game I made for AirConsole was also done the same way. I have 16:9 screen, but I saw AirConsole team played my game on very wide screen (don't exactly know the ratio - but was a weird one) and it fit as well.
Haven't read your tutorial yet —, Maybe I'm just repeating what you have written there. Just saw you're talking about resolutions and it's the ratio which is important.
Regarding resolution it's not really important because if you pick a bit bigger then engine will downscale it anyway. The same goes for small resolutions, engine will upscale it for bigger screens. Just remember to use bigger images for sprites if you pick low rez, so they could scale with good quality.
I personally pick an average resolution (1200x800) and use images of the 1.5x sprite object size. It scales nicely both ways.