Have a look at ProseMirror (http://prosemirror.net). It works quite well on Android and iOS and the maintainer is super responsive and has already fixed a lot of Android/iOS specific issues.
Edit: The landing page of the project does not seem to be optimized well for mobile. When on mobile, make sure to try the editor on http://prosemirror.net/examples/basic instead, as the landing page causes some unwanted scrolling for me on mobile.
Edit: The landing page of the project does not seem to be optimized well for mobile. When on mobile, make sure to try the editor on http://prosemirror.net/examples/basic instead, as the landing page causes some unwanted scrolling for me on mobile.