We were in Switzerland for 5 days last month. Took rolling carry on sized bags and were happy with that choice. We only used trains/buses. Yes, we rolled them over cobblestones and tram tracks. Think about whether you'll be comfortable with 15 pounds (or however much) on your back for long walks. We had smaller backpacks for the lightweight and frequent access stuff (passports, waterbottles, sunscreen, rain jacket, etc.) My 20 something daughter used a backpack for her Europe trip and was just fine, so I think either choice depending on your comfort level. But definitely pack light