Thanks, profdant139, but not so sure I am an "expert". :-) However I have been to the NR twice (had to go back a second time because we thought we must have missed something the first time there and came to the conclusion we had not) and the SR probably 4 times as many times as the NR.
I pretty much agree as stated above with the late May / early June or late Sept / early Oct. We were there once in March and got snowed in by a white out. (But also got some of my best photographs on that visit).
Profdant139 also makes the point that I often do - on the SR you are not looking into the sun for picture taking or just viewing. I will leave the NR / SR debate at that but there are a lot more points - but that is not this posting question.
To see some of my images go to
www.LaurenBarbara.com and to the Wanderings link on the left and then to the 2 Grand Canyon links. Some are also posted on
www.LaurensPix.com which is my "professional" site.
Whenever you go, spend a few days - it is at its majesty at sunrise and sunset - the colors and shadows make it breathtaking.