So why choose monogame, if XNA won't be updated?
MonoGame will be (and already has) started to introduce some new features beyond XNA. MonoGame is not tied to XNA anymore since just about full 1:1 code compatibility has pretty much been reached.
Now installed monoGame, and created project, and seeing that xna is included. So it use XNA libs?
MonoGame currently still uses the Microsoft.Xna.Framework namespaces, this will probably change in the future. The main reason why its like this is so people can port their XNA games over to MonoGame with less hassle. This means MonoGame does not use the XNA libraries at all.
Tried to give my friend realeased project, but only gets error.
MonoGame does have some dependancies depending on the platform, but like I said does not require XNA to be installed.
From what I know:
The current released windows platform, which uses OpenGL for rendering, also uses OpenAL, you can google OpenAL that and tell your friend to install that (OpenAL is actually installed when you install MonoGame 3.1. There should be no other dependencies needed. Once the windows directX platform is released the only required dependency that will need to be installed is .net 4.0/4.5.
Or maybe u have to suggest other C# game dev solution?
I think MonoGame would be a good choice, you could also use XNA, no problem with that even if its not going to be updated anymore (you can swap XNA -> MonoGame code bases easily anyway).
The only problem with MonoGame at the moment is that the content pipeline is still missing (I think it will be available soon though).