I have been there during the rally, and I have been there after the rally. I think it all depends on why you are going, party or riding.We have gone during Sturgis and also the 2 weeks before opening day, very different at Atmosphere.
If your good with thousands of bike in front of you and coming at you than during Sturgis week is when you should go, if you like to pull over and take in the beauty of the surroundings you should go a different week.