https://www.scirra.com/tutorials/73/sup ... reen-sizes
1. Use letterbox scale - design for any aspect ratio you want (easy, lazy, black bars)
2. Use scale outer - design to allow users with wider screens to see more of your background/layout
2. Use scale inner - design keeping in mind users with narrower screens will get portions cut off
Either way, I generally like to start designing with the squarest aspect ratio in mind.