I have the 70-200 f2.8L II and the 70-300 f4-5.6 non-L. The 70-200 is my most used lens (on a 7D), largely because it's sharp at f2.8 and I often shoot wide open.
The 70-300 is retired now, saving it for the kids to use. Now, there's a big difference between the L and non-L version of this lens, but I'll trade the extra 100mm for the speed and bokeh of the 70-200 at 2.8. It's liberating not be limited to f4-5.6.