Preferred gets you closer to the restaurants, south bus stop, and lobby. If you're on the Alligator Bayou side, you will get a Murphy bed, regardless if you're in a preferred room or not.
I can't recommend Andre's site enough. Take a look at all the pictures that are posted and all the info on the rooms. There are also maps that show you the location of all the buildings. Here's a link to the pictures of AB:
http://www.portorleans.org/gallery-POR-AB.php
As you can in the pics, it's one flight of stairs up to the second level.
I'm in the same situation, where I don't want to climb the stairs for our upcoming trip. It's just not convenient with a 2 year old and a stroller. I won't have a vehicle there.