We have several portables in the 12-16 gallon range and one small one similar to the Century in size. It was bought mainly for upholstery, nice size for one man to tote around. However the bigger units actually get used more since you don't have to dump and fill as often. Most of the cleaning we do with portables is commercial work.
We're out here where the ground is flat and plentiful......truck mount county. LIKE!
Seriously that limits our use of portables, with the hoses already in the home we just switch tools and we are cleaning upholstery.
Jarred you'll like the smaller unit it just works out nice for tight spots. We bought a plastic cart with good wheels and removable handle. Strap the unit on the cart, take our blue upholstery totes and you can wheel right into elevators or where ever you need to go in one trip.