I always used a backpack ... but I also often stayed somewhere in nature ... hmmm... and my experience says: if you only jump in a train with your suitcase, then leave it for the next hostel using public transports (subway, buses,...) it is okay...!
When you will not sleep in a hostel, only sightseeing the city, you can often use lockers in the stations where you can place your suitcase during the day. but it is sometimes really expensive... not unusually to pay 5 EUR per day...!
and in some cities, especially in Spain, I often had problems finding such lockers (reason: panic of terrorism/ETA) ...
and still something what I remember... only from seeing ... but suitcases seems really to work: watch the people from Asia/Japan visiting Europe. Most of them have suitcases - but also most of them uses taxis and hotels.
so for me, only a backpack is the real mean of transport... but suitcase is possible !!