I've gotta chime in too! I'm in favor of a break. We still have little kids, but when we went last year my hubby and I both slept about an hour while the kids slept too. It made the eves so much better. But you must realize, we were at RD at every park we did. We didn't plan the exact time of out breaks, but it seemed we'd be on the bus by 12:45-1:30 everyday. It was just time for us to go. Our breaks were usualy until around 4 PM to get to dinner or parks by 5 PM.
On the other hand, if you do not want to do breaks, 3/4 days work well too. BUT you need to take the night off then.
I'm figuring it will be hard to get 2 teens up in the AM for RD no matter what, but w/ long days - impossible.
GOOD LUCK!