This is a completely hypothetical situation that must be answered according to your morals:

Pretend that youre a photographer who has gone out to the Midwest to take pictures of an ongoing flood. Now as youre wandering around looking for a good shot, you see George W. Bush in the middle of a rushing river, holding onto a thin branch so he wont get swept away. The branch is about halfway broken, and you know it will break altogether in a matter of minutes. Now you can do one of two things: You can either rescue him or take an award-winning picture that will secure your place in photographic history.

Now for the question:

Which lens would you use?