I use a plain samsonite (if someone tells me how to figure out the model, I will have a look), which is made of hard plastic.
The downside is the weight, but it fully utilizes the allowed space, and as it has those clips to close I can push a lot inside, and close under high pressure.
Ideal for 3-4 days trips without checked luggage.
Also hard cases (if a normal shape) and decent wheels, are much more stable for long walks in terminals or when running to catch flights.
The extractable handle bar is also sturdy, and allows either to place something on top, or bedi'eved, if a little child is not in the mood for walking (without stroller at hand), to place him/her facing backwards, leaning his/her back against the handle bar.
Looks funny but does the job.