I agree with Paul and will add that it really depends on how much traveling you do or plan to do. If you only travel once in a while, go with what works best for you and what you can afford. If you travel more often, then don't go cheap - it can end up costing you alot more in the end. Cheap bags break and fall apart; something you don't want happening on your trip. If you're traveling alot, then spend the extra money and get something that will stand up to all the abuse.
We travel all the time and our Travelpro bags have been through alot of abuse, so the higher cost has been worth it.
What's interesting is that Europeans like the hardsided bags more than the Americans do.