The most popular type of carry-on luggage is probably the rolling suitcase. Rolling suitcases have many advantages-they are easy to transport through an airport, and they are easy to pack because they are usually semi-rigid, which gives them a nice square space in which to pack things like folded clothes. On the other hand they are usually not compressible (although the soft-sided kind do compress somewhat), which may make them difficult to fit into overhead bins, and they are also relatively heavy due to the fact that their internal frame, handle, and wheels. They also may not last as long as other types of luggage because the wheels and bearings can wear out and it is easy to abuse them by dragging them up stairs/etc, although high-quality suitcases should be fairly durable.
Rolling suitcases are often looked down upon by ‘backpackers’ because they just don’t fit the budget travel image, but I think that they have their place-I tend to go for them anytime I am not expecting to do a lot of walking with my luggage or when I am not traveling with a budget airline and am less worried about space constraints.
The other main type of luggage people travel with is travel backpacks, and in fact this is the type of luggage I use most often. My backpack is the Kelty Redwing 44 trekking pack, but there are travel-specific backpacks as well, which are basically suitcases with carry straps instead of wheels. In either case, the biggest advantage of a backpack is that they are easy to carry long distances, especially over rough terrain. Most large backpacks have an internal frame, which transfers the load to your hips, making them relatively comfortable in this application.
Another advantage of backpacks is that they seem to be less scrutinized by gate agents. Although probably not the right thing to do, I have often overloaded my backpack-sometimes significantly so (20+kg), but by simply pretending that it is light gate agents seem to think it is lighter than it really is. The same is true for size-although my backpack is at the limit of an acceptable carry-on size, I have very rarely been asked to place it into a sizer even in cases where most passengers with suitcases have been asked to do so. And even in cases where I have been asked to size my backpack, it has usually not been a problem because it is so compressible.
For me, the biggest disadvantage of backpacks is packing. I personally think suitcases are easier to pack and more space efficient because backpacks don’t hold their shape, but on the other hand it is easy to roll clothes and stuff them in, which is often touted as an advantage. This is a solution which works well for casual clothes but doesn’t work at all for anything remotely formal.
The other disadvantage of backpacks is that they are heavy to carry. Internal frames certainly help, but the fact of the matter is that at the end of the day, it’s you supporting the load instead the ground, which can be tiring. However it depends on the situation as well, because while rolling suitcases are good for smooth surfaces, they are not suitable at all for use on gravel/off-road.
In the end, the type of luggage you choose really depends on your situation. For people who either don’t walk a lot or spend their vacations in cities, I think that rolling suitcases are really the best choice. They are also the best choice for anybody traveling with formal clothing because they are easier to pack neatly than backpacks. On the other hand, backpacks are better for people planning on walking any distance away from smooth/flat surfaces. Personally, I think that backpacks are more versatile and use them in most situations, but for things like family vacations, where we usually have a car available, I generally switch to a rolling suitcase.