I've had the 70-200 NON IS. IMHO its superior to the IS version. I don't know why. Perhaps its having fewer elements to intefere with the light path.
I would also suggest purchasing an older version from aroung the mid-90's to early 00ies.
The 70-200 was introduced to replace the 80-200L (a VERY underrated lens) and primarily intended for photojournalists, so they had to be (and were) real corkers. If memory serves, IS came in around 97/98 (?).
The non-IS seems to me sharper, to have more 'bite' and better (more natural)colour.
Plus its a lot cheaper used.
But you won't go wrong with either.
