Welcome to Flyertalk, Halcyon Days. In my experience (most recently, this week), the aircraft is a 757-200. I believe I would opt for the first row as your parents will not have anyone reclining in front of them, and access and egress will be easier. Moreover, row 6 is the last row and may not offer as good a recline (but I am not certain of this). I would select Row 1. As time goes on, just check their itinerary on line and you may be pleasantly surprised that seats will open up in other rows and you will have the ability to change the seats online at the DL website.