I travel 50-70% for work (long distances and long duration) in trips with 2 or 3 flights. I carry a pretty full carry-on so I can manage when my checked bag doesn't arrive. I use a duffel bag with separate wheels because it's got lots of room. Lately though the airlines are forcing me to check the wheels and carrying around that heavy duffel from terminal to terminal isn't working. So - I recommend a bag with wheels rather than solving the problem with separate wheels. And I'm in the market for an international trolley carry-on.

I appreciate all the great advice I'm finding here.