As for a carry-on suitcase, go for soft but durable one. Durable enough to wheel around and soft enough that it would be easy for you to fit it in the overhead compartment. Just make sure that your carry-on luggage is of a good quality.
Make sure the interior suits your style. Even the smallest details like the zippered pockets, number of compartments, design, color, etc.
Be keen about the luggage wheel types. You can choose between skate wheels and spinner wheels.