How much milk do you get from each pumping session?

Hey moms! How much milk do you get from each side during a pumping session? I have an Ameda Purely Yours through insurance but lately I've felt it to be lacking in power. 
I go back to work soon, and want to make sure the pump I use gets the most out in the shortest time possible.  As such, I'm thinking of the Medela. Is this worth it or should I just stick it out with my current pump?