What is the best time to go ( least crowded)?
I've gone a couple of different times (for more than a day trip), and none of them were extremely crowded. These were in mid-January, end-May, mid-April. I think the most crowded time was in April, but that was because the last half of our trip coincided with the world dance and cheerleading championships. I would definitely suggest NOT going during that time.
I do know that if you want low crowd levels, you will want to stay away from holidays, such as July 4th, Memorial Day, Spring Break (which goes for a couple of weeks since Spring Breaks are different in different regions). I don't know about Christmas or Thanksgiving, as I've never been during those times.
Hope that helps some.
It might be more helpful if you would give a few dates that you are interested in going.
allears.net is an