I've never been on the Fantasy, or used a rollaway on a ship. But I have used a rollaway elsewhere, in the past, and I would avoid it if at all possible. They have never been comfortable. They also take up too much floor space, making moving around the room in the evening and at night very difficult.
Where as the upper bunk will take up no floor space and will likely be just as comfortable as a lower bunk. From what I've seen of upper bunks the mattresses are the same as for lowers, and will obviously have a firm base since the mattress rests on a solid surface. Not something that folds.
I would insist on a quad room. I would not consider the rollaway good enoungh, and would not accept it. Of course, remember if you booked a guarantee, you take whatever you get. But if it's a regular booking with an assigned cabin, I would not accept this as our assigned cabin.
