I'm jealous! I waited in line overnight at the Bethesda Row store overnight last year. I didn't want to ask my husband to take of work again this year (we have little kids), so I just preordered this time. But I had a blast, and want to do it again!
The Bethesda Row store is a great place to wait in line. It's a good area, with lots of sidewalk traffic. It was fun answering the questions from people walking by thinking we were nuts. It got pretty chilly at night; be sure to come prepared! I wouldn't just bring a blanket; bring a hat, warm socks, gloves...
I wouldn't go to Montgomery Mall. Unless it has changed from last year, the mall won't let people wait inside, and I think it would be boring and creepy to hang out in that parking garage.
Last year I got there around 9 and was about 7th (?) in line. I had wanted a gold 32 GB iPhone 5S, but wound up having to get the 64 GB instead. I don't think they even had any gold 32GB there.
Good luck! I hope you have a great time!
Laura