I've been there twice. Very sobering. If you can visit only one camp, may as well go to Dachau as it's near a large city and readily accessible.
On the second visit, we took a city bus out from Munchen on which there also was a large group of teens of swarthy Mediterranean appearance headed to the camp. I guess their teacher was with them. They were loud and obnoxious, bouncing around the bus, sticking their faces in other people's faces, etc., when an elderly German woman started berating them for their rude behavior. From what we could understand, she said (in German, of course), "There is no place in Germany for foreigners!"