It's for two adults and a 4 1/2 yo boy (who loves to swim). We're think POLY but have never stayed there. We don't care whether we have a monorail or not. It's definitely a perk but we're accustomed to staying moderate so that doesn't really matter too much for us. We just want a nice, CLEAN, modernized room.
If you are only taking 1 child, I would also strongly suggest getting a studio that has the pull down murphy bed, so you can leave the sofa as a sofa. The studio will feel much larger that way.