For us, we liked doing the rim to river and back in one day (down S. Kaibab and back up Bright Angel) because we aren't really campers, and it kept us from having to carry a lot more gear, which would have made for a less fun hike. We were able to carry mostly just water in our daypacks, and although it was hard, it wasn't crazy difficult since we'd trained well for it in the NC foothills and mountains. We also did it on a day that was not super crowded (May 1, 2006, before school is out for the year), so we only rarely had to look at anyone's heels. We started out at 7:00 am or so and were done before 5:30 pm (can't remember exactly, but it was still plenty light).
The beers and food tasted REALLY good at the top, too.
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow