I've been debating between the 70-300 and the 70-200 f4 is. Now that they are equally priced, it makes the decision that much more difficult. I have shot the 70-200 f4 is and on occasion wished I had more reach, but who doesn't?
If you're going to be using the lens outside, then the 70-300L is a fine choice. I like it for travel, zoos, etc. The question is whether or not you can live with a sllightly slower lens at the longer end.