I recently implemented Google Play billing in my app (after doing Stripe and Apple App Store) and Stripe was by far the easiest to implement/test/maintain. Google and Apple not only take their 15/30% cut, their payment systems add a very non trivial amount of work (cost) to implement and maintain while offering none of the (automated) testing capabilities of Stripe. Work that I'm forced to do, even though I had already implemented Stripe. All because they have a monopoly on their platform.

For something as critical as payment processing, both Apple and Google make it an arcane journey into API documentation and stack overflow questions. Hoping to write a blog post detailing all of this in the near future.