I'm really interested if anyone has advice on the best cross platform 2d focused game engine?
But if you are going for a 2D game, I think Defold is a really good choice. We support Android, iOS, desktop (Win, OSX and Linux) and HTML5. We try to solve all the icky platform specific stuff for you. And to start coding you only need to download the editor, there is no development environment to set up.
Are you doing fancy 3D stuff, then Unity will probably be better, currently. :)
Still, new 2D engines are welcome as Unity still has the 3D package to work with in a 2D game.