I have a 65L Osprey Porter bag. We don't intend to do that much hiking, but we'll be moving from place to place often and the unloaded weight of the pack is just fantastic.
I traveled all around Europe with a 46L Porter in late 2014. All in all, it was a fantastic experience, but I also had my Tom Bihn messenger bag with me. While I like my Tom Bihn bag, I'd rather not have two. In order to collapse a bit more gear and all of my electronics into a single bag I regretably needed to bump from the 46L to the 65L. The bag, despite being significantly more spacious feel almost the same when empty.
That's it for a whole year. Wish me luck.