Ed himself said there's no performance difference between the cylinder subs and their equivalent box sub. The difference is one of construction. The cylinder is made of dense cardboard covered with a velvet sock, and is thus quite lighter than the box sub. I'd guess the velvet sock is less expensive than the wooden finish on the Ultra also. Thus the difference in price and weigth.
As to which to chose, it's a question of personal preferences. The PC will basically look like a black water heater. The PB has basically the size and shape of a mini-fridge, but with a nice wooden finish. The PC uses less floor space but is very tall. I know in my case I'd choose the PC because it's cheaper, lighter, and more easily placed into a cluttered living room. Also for hearing people say things like "where the hell is the sub that produces *that*" (i.e. the PC can be hidden in plain sights because people expect big boxes) or "what the hell is *that*" if they happen to notice the aforementioned water heater-shaped monolith.