Every year I see students battle with too large, too heavy, and super cheap luggage that they drag (or end up pushing or kicking) from city to city. Remember when traveling around Europe (especially on a study abroad program or on group trips) you often have to carry your luggage a couple blocks (since large buses can't fit down small streets) and up flights of stairs (since many European elevators are tiny, or there are 30+ people trying to use it at the same time).
I recommend investing in three pieces: 1) a large checked bag (27-29 inches), 2) a carry on bag (20-21 inches), and 3) for the ladies, a tote or larger purse for the plane. Now this is the important part, all pieces should be able to attach to one another. Trust me, this will make your life so much easier!
Here is what I use:
If travel is not a part of your profession or something you do often, you don't need to invest in a premium luggage brand like Briggs & Riley (although from my personal experience, I cannot say enough good things about this luggage). For my career and lifestyle these pieces were a worthwhile investment (still in perfect condition, ten years and countering!). But you can find similar, less expensive, and just as functional options. I recommend Samsonite and Travelpro, and here are some options:
One last tip - many luggage companies are now offering 20" wide-body international carry ons. These bags are slightly larger to give you more space, but because they are wider, not longer, they still easily fit in the overhead compartment. I highly recommend them for international travel!