If you already have some developer background, I suggest not to take any courses.
When I have an idea and I want to learn a new language or framework, I go and try to implement that idea in the new environment. One example could be the previous version of my blog. It was a (bloated) Symfony app; I wanted to learn Python. So I rewrote my blog in Python using Django. Today Python is my $job.
If you already have an app idea, go and write it. Do a very beginner course only to learn how to set up a development environment, how to compile your project, and how to debug your app while running it in an emulator or on your phone. Then create small tasks to implement, and by the time the app is ready for a beta release, you already know Android development (to some extent).