a PC12NSD can easily be moved by a single person, but the plus and ultras, not without some creativity (don't try to spin it like a drum on a hard surface, unless you don't like your floor)
i like the cylinder i have now because it doesn't hurt as much when i bump into it (and it happens a lot)
i like that it only eats that small footprint in my room.
i don't like that i'll need a vacuum instead of a rag to clean it. but it's no biggie since i don't do the cleaning anyway.
i came from using the box ultras to this cylinder ultra. and looking at the box ultra again at a friend's house ... hot damn, that box is massive.
performance wise, i don't notice any difference (aside from the fact i went from 4 boxes to 1 cylinder)