People opinion will vary depending on MANY things. Pure comfort, what they carry, and possibly most important... riding position/bike type. I ride a road bike and more often than not, my track bike... both have significant saddle to bar drop, but not TT type setups.
For ME, a low backpack is uncomfortable. If it's higher, the weight sits on my back instead of hanging off my back and pulling on my shoulders.
With that said, my shoulders didn't like 2 strap bags... but I ride every day with a messenger bag hiked up nice and high/tight. The one strap, and fitment just works for me.
I hate the feeling of a "heavy bike" so I avoid racks/panniers/etc... but am debating a small rack for a few trips. The big bags just encourages me to bring lots of extra crap along for the ride
