I let the type of trip determine whether I bring a backpack or a suitcase. In fact, a backpack or suitcase can go with any type of trip. But in some cases there is a practical difference.
On a trip where I only go to 1 or 2 hotels. Or if I go by car, I often choose a suitcase. A suitcase on 4 wheels that is.
A suitcase is more organized with packing and unpacking. Even if you don’t unpack a suitcase, it is still more organized than a backpack. With a backpack it may be that you always have to have the bottom.
For an overview, both a suitcase and a backpack packing cubes are a godsend.
If I travel longer than I travel more often, then a backpack has my preference. I then use public transport. Possibly even a boat. So I walk more and longer. Not all streets are equally pleasant and smooth. You encounter more stairs or you have to climb in and out of a boat. Or walk on a sandy beach.
Another advantage of a backpack is that you have both hands free. To have your phone in hand for navigation. You can pull up on brackets to climb onto a train.
Weight. In both cases you will have to pull the suitcase or hoist the backpack on your back and walk with it. Many people find a suitcase towing less than the weight of a backpack on your back.
A backpack is made of more flexible material and is therefore easy to cram in even worse or under a seat on public transport.
In a suitcase you transport fragile items better and safer and you look less like a traveler.
Whichever you choose. Buy good quality.
I have a small backpack as hand luggage anyway. A small backpack is doable with a suitcase. With a large backpack, I put the large one on the back and the small one on the stomach. Like a turtle.
Choose what makes you feel most comfortable. If there is a time that is less pleasant, you will not be disappointed if you have listened to others.