I'm making a game for android and would do it in 720p, but the phones got all different aspect ratios. Also thinking about a ios and windows phone port later.
When the aspect ratio does not match, pretty much all I can do is making black borders, stretch it, or leave the part which does not make it out on the screen. The game would be not as good when not the entire screen is visible, for example you see an enemy spawning later.
Which aspect ratio should I choose? On the techniques I stated above, maybe I just let the user decide, they are very easy to implement and they can choose the handicap which is at least annoying for them.
On 16:9 they will be only borders on the top and bottom, but at some aspect ratio somewhere in between, some would have them on the left and right.
Resolution itself is not important, trying to scale down with drawing to a renderTarget first.