dreamon

Those super light fold-into-their-own-pocket backpacks that you can get in places like Kathmandu are great. I use mine whenever I go hiking, to the beach, the market, etc. and shove it in a corner of my case when not using.

happytourist

Re four or two wheels: On flat surfaces such as airports the 4-wheelers are convenient, but they have significant drawbacks on regular sidewalks. The wheels are smaller and are outside of the base but are included in the overall dimensions of the bag, resulting in a smaller bag. Two-wheeled bags use skateboard wheels and are embedded into the bag, making for both stronger and larger bags.

RM67

You can pull a 4 wheeled suitcase along on 2 wheels on any rough surface so the points about 4 wheels being disadvantaged are totally moot.

I would go for the Cosmolite - they are very durable, very light, and you are much less likely to bash anyone in the face with one on public transport than you are with a backpack.

dreamon

RM67, I am SO tired of hearing people complain about the careless behaviour of those using backpacks. I have been inconvenienced many more times by those hauling suitcases. It doesn't matter what kind of luggage you use, people need to take care that they don't cause problems for others. And they nearly always do.

RM67

Maybe the reason you hear about it so often is because a lot of people with backpacks aren't considerate. My personal experience is that a significant number of people wearing them are oblivious, backing into others because they forget they have something sticking out from their back, and hitting people who are seated in the face by turning round in the aisle with them still on.

People with suitcases can be annoying if they stop dead in your path to faff with them, or when they're trying to fit them into small spaces or can't lift them into luggage racks, but I don't recall seeing or hearing of them causing physical injury to others with the frequency backpacks do.