I never own 200mm prime, but I LOVE LOVE 70-200mm f2.8 IS II. I have version I and decided to upgrade version II, due to $300 instant rebate from Canon plus $100 from B&H ($400 of saving, $1974 plus free shippping)
I use it on my 60d, results are GREAT, even at f2.8.
On 5D II, which I'm borrowing from a friend, this lens creates SUPER blur background.
I plan to buy a used 5D II for now, until 5D III comes out.