If you're heading out for a long trip, no other type of luggage beats a rolling duffel bag for capacity and convenience. There's plenty of room for your belongings, your partner's, and all the stuff you find along the way and can't resist taking home. Look for ones with a wide opening for easy access into the bag and separate compartments to stow shoes and dirty laundry.
Strong yet lightweight, Eagle Creek's 30" x 17" x 12" HC2 Hovercraft is sleek and solidly built. The duffel's "off-road" wheels provide a smooth ride over terrains rougher than an airport floor. And exterior compression straps keep the load inside this rolling duffel secured. I also like Eagle Creek's "No-Matter-What" policy: If the luggage is ever damaged, the manufacturer will repair or replace it free of charge.
One of the sleekest rolling duffel bags around, this 30" x 15" x 14" model from Travelpro is light and tight. The zippered compartment on the side is handy for packing last-minute items and things you want to access as soon as you exit a plane, such as a winter coat for the trip home. Roomy and well-constructed, the center compartment can hold a large amount of gear.
When I shop for a rolling duffel, I like to read the product reviews. At this writing, this High Sierra Wheeled Duffel had 26 out of 28 buyers who would purchase it again. This big boy measures 32" x 15.5" x 14.25" and comes in cool colors. As an aid to packing, this highly rated rolling duffel has separate zippered compartments.
Traveling for a while and need more room? The biggest wheeled duffel made by Samsonite, this well-designed, 36" x 16" x 16.5" bag may do the trick. What you need to caution against, though, is putting too much weight in it. Airlines have weight restrictions on baggage, so know before you go -- and use a luggage scale before you go to the airport to make sure you're not "overweight."