Starting in 11th edition.

Hello, i have read the beginners guide.

I would like to start a raven guard army and play with a friend who doesnt mind which army.

Is it best to start with a warhammer 40k getting started space marine.

Or buy the armageddon box set or start with a battleforce.

In which way is the best to start with a small army and have all the right rule books and assescories to start playinf ?