Tri Girl - I would second going to the North Rim. It's cooler and quieter than the south rim, especially during the summer.

My DH and I just got back from a week there last month. We didn't do that much hiking, in fact very little because of a bike accident on one of the trails -- if you plan on renting one of their bikes check the brakes first!! The front brakes locked up on my rental and off and over (the bike not the canyon rim ) I went. That happened on our first day so not much hiking after that.

Still was a great time though, just so incredibly beautiful and remote. I love it and can't wait to go back with one of my own bikes!

Susan