Soft-side or hard-side? Soft-side bags are generally lighter, more vulnerable to cutting or slashing damage and less expensive; hard-side travel cases are often heavier, more expensive and may permanently deform or dent if they receive sufficient abuse.
Wheels or no wheels? One-bag-travel experts tend to recommend bags without wheels, as they are lighter and have more carrying capacity. If you do choose a wheeled bag, look for encased wheels set widely apart -- they maneuver better and are more stable. Check your wheeled bags for balance, too; one common complaint about rolling bags is that they tend to fall over instead of standing upright. Larger wheels will maneuver more smoothly over uneven terrain, and softer wheels will lessen vibration and noise.
How are your shoulders? If you're opting for a non-wheeled carry-on, are you prepared to carry it over your shoulder or in your hand for the entirety of your trip? If not, consider convertible models, which have tuck-away backpack straps to let you distribute the weight more evenly.
How much do you pack? Most airlines charge baggage fees by the bag, so it's usually better to opt for one large checked bag instead of two smaller ones. The exception to this is if your bag goes over the usual checked bag weight allowance (typically 50 pounds for domestic flights) or exceeds the airline's size restrictions. Checking a second, smaller bag might be cheaper than paying extra fees for an oversize or overweight bag.
Do you need internal organizers? If your suitcase doesn't have many internal organizers, you might consider using packing cubes or stuff sacks to help keep your belongings organized.
Air travel is becoming ever more expensive and restrictive when it comes to luggage. Airlines charge you to check your bag, but limit the size of a free carry-on to a size that isn't practical for more than a short trip.
If your carry-on is too big or too heavy, you might still be faced with unexpected fees and the hassle of an unplanned bag-check. Play it safe by keeping your carry-on at 20 pounds or less and below the typical maximum size of 22 by 14 by 9 inches. European guidelines are sometimes more strict. About.com's guide to honeymoons and romantic travel, Susan Breslow Sardone, provides a list of carry-on size and weight limits for many international airlines -- but you should still double-check with your airline, domestic or international, to confirm their most up-to-date requirements.
Also, keep in mind that some luggage manufacturers list the internal (packing) measurements for their bags, but airlines go by the external measurements. Unless otherwise noted, all measurements listed in this report -- excluding the numbers you'll see in bag names -- are external measurements.
If you're traveling in a group, planning for an extended stay or have to bring heavy or bulky belongings, you'll need to check at least one bag. A little research can help you dodge, or at least minimize, the costs you incur. Start by shopping airlines when you buy your tickets -- if multiple carriers allow similar fares, check to see which has the most generous policy for checked bags. At the time of this report a few carriers -- namely Southwest and Jet Blue -- still offer at least one free checked bag.
While you're at it, check into loyalty programs. Sometimes joining a frequent flyer club, applying for a credit card tied to said frequent flyer account or reaching a certain number of frequent flyer miles is enough to get you at least one checked bag for free. Do read the fine print on any luggage policies -- size and weight limits still apply, and if you go over in either case, you can expect to pay extra fees.