I have tried both rollaboard and backpack travel pack type of bag.
I much rather use the backpak
I used the rollaboard in Europe for 3 wks and with so many steps etc, I thought it was a pain to have. I ended up lifting the rollaboard a million times.
Since then I have used the backpak from REI , called a travelpak. It is similar to the Rick steves bag. In Europe so much easier. I can beat people to passport controls by going up and down steps instead of escalator and also some hotels dont have elevators.
Also some countries, the sidewalks have so many potholes it is so much easier to use a back pack. And as other people said it is so much easier to fit in the overhead bin of airplanes than a rollaboard.
I work for an airline and I have never seen anyone ever have to check a backpak or soft sided bag. It is always a rollaboard.