I'm hoping we'll be able to go this November.
The only things I know: my parents like the North Rim more than the South Rim, but it's a little harder to get to. I think there's only one hotel on the North Rim, but there are, like, 6 or 7 on or near the South Rim. I know that there's one portion of the South Rim that if you go during certain times of the year (I *want* to say May through Oct, but it might start earlier. I know it ends in Oct), the only way in is their tour bus or hiking, no private vehicles allowed. The remainder of the year, though, that road is open. I don't know if there's anything like that on the north rim.
You can get a good feel of the place in one day, but to really, truely experience it, you need at least two, even just to do the rims. We're only going to have about a day and a half when we go if we can go.
When to go really depends on your preferences. Summer months are easiest for most people's schedules, but that's also the hottest time of the year and the Grand Canyon can get hot. Spring tends to have more water, not that I remember being able to see more than a few glimpses of the water at the bottom of the canyon. But if you're going to try and do any of the hiking, donkey rides, or rafting, the extra water can be nice. Especially if you're going to one of the mini-waterfalls.
Fall I'm not sure, but in Winter the North Rim is closed due to snow. South rim is still open. I've seen pictures with a dusting of snow on the canyon walls and stuff and it looks beautiful. We're hoping that if we can go in Nov, there'll be a touch of snow.
The official website is at
http://www.nps.gov/grca/index.htm and there's another one for just the South Rim hotels at
http://www.grandcanyonlodges.com/
