I've always found a backpack to be the best type of luggage to use when travelling....unfortunately the wife insists on using suitcases which I find a bloody nuisance to be honest.
Oh.....the days of being free and single.

I'm sure you are already aware of the advantages of being able to shove it on your back when walking any distance, having your hands free at all times and the ease of stowing it. I see the only disadvantage of it being the chances of getting crumpled clothes......which can be overcome if choosing the right clothes.
To me a backpack gives the impression of you being on a adventure rather than just a hotel hopping tour.