how tall are you?
its really important thant if your in the pool you can cover your belly when sitting/kneeling/on all 4s.
i had a hard sided one which was HUGE and i had to go on tippy toes to get over the side and have my head on the edge and my feet didnt touch anythingon the other side. (but this pool was a special made one for my mw)
for me i liked moving about in the pool so the square would be better for me.. although corners seem wrong