i love my pac ultimate deluxe. the x-strap is beautiful when i have a heavy load and it's always comfortable no matter what.

as another poster noted, messenger bags are designed to be most comfortable under load when you are riding your bike. i've had mine on a couple of times just walking around and even just the weight of the bag itself can be tiring. if this is a concern for you, i suggest you take the others advice and go for a backpack.