Yes, MonoGame is the oldest and most mature project, but it is pretty low level. The DeltaEngine does not really care if you use XNA, OpenGL, DirectX or frameworks with the same API (MonoGame, ANX, it tries to work with those frameworks, not against it) or any framework on top (SharpDX).
Delta Engine is still early in beta, but for those who want to try it out a release is coming later this month, which supports Windows 8 and Windows Phone. While in beta Delta Engine is also free to use for everyone and any beta platform, so why not try it out and see if it helps you.
Disclaimer: I was an XNA MVP from 2006-2010, also some of the ANX guys are now working for the Delta Engine. And I am the CEO of the Delta Engine ^^