I'd take the 135mm f/2..
To me its more versatile than a zoom, for a long time I used its big brother, the 200mm f/2.8 just fine with no problems....if that was the lens i had, and i wanted to take a picture of something, I found a -way- to get that picture...
Sure sometimes it sucked [Not encouraging i know] but hey, I got creative...
I'd take subject isolation ability and speed over focal length versatility
Keep in mind if you want environmental, you can stop the 135 down easily, whereas you cant open the 70-200 up farther than f/4 to get more isolation...
That said, IS can give you an interesting method of isolation in a busy space....

Because IS shows subject movement, your background can be a blur of people....its somewhat interesting sometimes...
Cool shot - environmental shot with subject isolation - interesting!
Thanks everyone for all your suggestions now just got to decide which camera bag to take.....
Happy 4th July to all our US POTNers!! My 24-105L is currently on holidays enjoying a beach party in San Diego as I type.. (without me) 



