Getting a pixel / texel / point from a buffer!

I need to know what object I’m clicking on with the mouse, and getting an index from the stencil, or an integer buffer is a lot more simple than setting up all kind of structures and calculate intersections.
What’s the simplest way to get a single point from a buffer, so that I get it’s value?
I’m thinking in setting up a double buffered pixel buffer and use glReadPixels. Is that the best (faster, non blocking, etc) way to do it?

Thank you in advance.