I carried a Maxpedition Colossus for years. It never was too comfortable, but I put up with it for quite some time. I still carry it from time to time when it is the most appropriate choice, but it has really made me a fan of backpacks. Having all the weight bearing on just one shoulder really gets tiresome. Even 10 pounds will feel like a lot more after a few miles.
Unfortunately I carry a backpack with all my work gear (laptop, iPad, files, cables, etc.), so I can't really carry two backpacks while travelling through airports, etc. Therefore I've been using an Osprey messenger bag, which seems to carry the load better than my Colossus did, even with more gear in it.
If I ended up having to hoof it on foot I would bring both my backpack and my messenger bag, but the laptop, iPad, work files, etc. would not be coming with me.