I used to carry a plain black, large messenger bag. The strap across the body could sometimes, depending on load, make the chest look "bigger" (in the bad way).
The uneven load was really annoying, but it was easy to access. And it looked cooler.
I eventually ditched it for a backpack. I have to carry a huge amount of (quite heavy) stuff, do a fair bit of walking, and climbing in and out of trains with it (from the ground, not the platform).
Although I preferred the messenger bag (it was more my "style" - more subtle, more casual, less sporty), the backpack is much more fit for purpose.
If I need a casual bag on my days off - I take the messenger.
Everyday work? Backpack wins, hands down. I can take my hi-vis over-the-head style vest off and put it in the backpack without stopping walking or putting down the bag. It's all just practice
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I think it all depends on what you're doing with it. How far you need to walk, what you need to carry, how often you need to access it on the move, etc. Find your priorities and you'll find what you need.
At the end of the day, the most masculine bag is the one that is functional more than fashionable
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