I always vacillate between buying good luggage and buying cheap luggage.
We bought a good set of samsonite, and it's holding up pretty well, but I hate when I see the way the airline baggage people throw the luggage around. I know that they can't handle every piece as if it was fine china or nobody would ever get anywhere, but I have really seen some of them throw luggage around when it was not necessary to do so.
I generally look for ballistic nylon (resists punctures/tear). I look at the handle & the zipper to make sure they look pretty strudy. I look at the wheels to make sure they look pretty sturdy and don't stick out too far from the "body" of the luggage so they can't snap off. If you can find it in an odd color, that he;ps, because then you can see it better coming off the luggage carousel.