I recently did some research on this. I narrowed my choices to the Delsey Helium Aero and the TravelPro 21" MaxLite 4. Costco has a Delsey set, though I don't know which model, in stores right now for like $120 or so.. I ended up deciding on the TravelPro because I really liked the duochrome coloring and reviewers were saying that the Helium Aero was actually a bit bigger than 21" and wasn't fitting on a few airlines. Also, because it is "shiny" it is prone to show scratches (although it IS so pretty - lots of cool colors!).
There are SO many luggage choices out there! I kept my search in the mid-priced range and tried to find the best quality. Hope this helps.