I'm a contractor/freelancer so when I hire people I'm hiring individuals to do specific jobs for me, not taking on employees, but I'll explain the way I look at it:

As a software developer, what counts as experience?

Fingers in code, brain solving problems.

Can you include self taught as experience?

Absolutely, as long as you have any code at all to show for it, and you can demonstrate that you learned something from having done it.

or developing a project as experience?

absolutely! As long as there is code and your fingers were in it - it counts!

or Should it be working in many companies as software engineer?

This is good, but personally I'd rather hear about the projects where you had creative control, not just one of many labourers! I feel you learn better lessons when you try to make decisions about more parts of a project or codebase. I don't expect you to master everything, but building projects where you touch all parts of it will help you work closely with others on larger projects where roles are more clearly defined.

I'd almost value the self-projects as better experience than time spent in an office as a software engineer.

Watch for my story on the CV. It should be finished soon. I'll edit this with a link once it's complete.