Canon 70-200 F4 IS vs 70-200 2.8II IS

I owned the 70-200/4L IS at the same I owned the 70-200/2.8L IS mk II and borrowed a friend's 70-200/2.8L IS mk I.

The mk II is definitely superior, even wide open.  It's definitely very SHARP; much sharper than the mk I.  I don't hesitate recommending buying the 70-200/2.8L IS mk II.

My personal big mistake:  I sold the 70-200/4L IS over the idiotic guilt of spending all that money.  There's times when I would have really preferred lugging the f/4L IS around vs. the f/2.8L IS.