Wheels on luggage is not a new idea, because it's a good one. Especially when trunks were made of wood and the clothing inside was made of cotton, wool, and linen, picking it up was to be avoided. However, the kind of treatment dished out to such baggage meant that the wheels probably wouldn't last long.
When inline skates hit the market in the 80s, luggage manufacturers realized these were just what they had been looking for - a smooth-rolling wheel that was nearly indestructable. Almost immediately, luggage without wheels became hard to find.
So, as you're shopping today, the details of the wheels of themselves are almost irrelevant - as long as it's a respectable brand like Patagonia, Eagle Creek, or North Face, you can concentrate on the rest of the bag- it'll keep rolling. Regardless of size and design, there are some elements to check out as you compare models:
Durability - Look for a tag identifying the use of Cordura nylon, widely recognized as the most durable fabric available. You wnat the bag to survive being dragged across a parking lot or two.
Water resistance - The body fabric should be shiny on the inside. This indicates a polyurethane coating that will keep water from penetrating the whole cloth. Unless all the seams are sealed, however, the bag is not waterproof. Some brands will design the bottom to reduce stitching and this can greatly increase the protection offered when your bag is dropped in a puddle. You might see reinforced vinyl and it is inherently more water repellent so the fabric won't gain weight when soaked, but it's shiny, heavy and will leak at the seams like a conventional bag.
Longevity - Compare the size and weight of the straps and hardware. Wide, well-padded handles, big zippers, and reinforced stitching indicate a bag built to last. Lighter bags are frequently built with thinner fabric and fewer pockets or inside accomodations, and though the fabric might hold up, if you really like mesh dividers and pockets, it might be worth going for the higher-priced option.
Ease of Use - Test out the handle as if you were trying to answer the phone, find a pen in your purse or pocket, and needed to haul your luggage along behind you - how well can you steer the bag, and how confident are you that it will maneuver the way you expect?
Size - It's easy to put just 20 liters of stuff in a 30L bag, but will you stop there? How much will it weigh when full? Do you really need that much bag? 'I've got room for that' might lead to an overweight fee at the check-in counter, and maybe a hernia in the rental car lot.
The general rule of thumb for luggage is that when you add up the three dimension in inches, the result must be 45 or less to qualify as carry-on. The corollary is that any bag with a longest dimension over 22 inches won't fit in the overhead bin. The benefit of a smaller bag is that you will bring less stuff, which means packing and unpacking are easier and the load is lighter.
When looking at rolling bags, you'll see a number on the model name or tag, which indicates the longest dimension of the bag. This doesn't mean all 28 inch bags are the same volume. Whenever possible, find the actual volume so you can compare apples to apples.
Weight - Consider that you'll be carrying your stuff in the bag, and more luggage weight means less stuff weight. However, as touched on above, the lighter bags will be less substantial, have fewer dividers, pockets, straps, and reinforcements. While the heavier bag will offer more protection for your stuff, is it worth hauling another pound -or two- that is just bag? Some brands are expert at providing excellent features and durability at very low weight, but the craftsmanship and materials they use are costly and will be reflected in the price tag.
Whatever your decision, keep in mind that the value of quality will remain long after the satisfaction of savings fades.