I did it for the iPhone 4. While I had a great time, I wouldn't ever do it again.
I did it for the iPhone 5. First time I've ever stayed up all night and it was a very good time. For the 6, I really don't care if I get it the first day. Maybe that's because I had my first iPhone 5 for a few weeks then returned it to get the 32GB version. That reset my upgrade date so I'm not due until October 18th. I'll probably be getting a new phone that day or a few days later. It will give me a chance to compare the two sizes and see what the reviews are.