I stayed in Polwarth House for my second year. The rooms are very much the same size as the other Halls - if anything, they seem smaller as the desk runs along the side of the room and doesn't leave much floor space (ASH and AKD might be the same - I spent my first year in Murray, where the desk is along the front of the room by the window).
That said, I really liked Polwarth. The flats are all either 4 or 6 people, which is a good number if you don't fancy sharing with loads (although to be honest, that was never a problem for me). The main advantage it has over Ally Court is that it's more "immediately" on campus. You're about 10 mins (at the most) from your classes, as opposed to at least 20 mins from Ally Court. Also, Polwarth houses the main laundry facility, so you'll be right next to that.
I have photos of my old Polwarth flat which I could e-mail you if you're interested. Getting a room there could be tight though as I think there are only about 100 spaces.