For Barnyard Politics, I used AndEngine. Since then, I have used and loved Unity3D for hard core conceptual prototypes and am in love with Construct 2 now for my current side project though. I am walking my kids through developing and I needed something less complicated than Unity3D. Construct 2's dev environment is fairly easy to use and it exports to html,css, js. Better than that is that I can make my own plugins in js and make them available to people that will create content for my future website / app. I have extremely limited non-corporate time so I plan to author the first content to get started but then make tutorials and allow others to create.

Note: My opinions on game SDKs or anything else here are entirely my own and have nothing to do with my role in the corporate world. The experiences I mention here stem from the fact that I cannot stop programming or thinking about apps when I come home. I love this stuff. And yes, I deeply desire to get to MRR at some point.