I've had a similar journey as the OP did. I was messenger bag user, had an injury, switched to panniers for awhile while I healed, and then went to a backpack.

It's a good thing that there are as many options as there are. Personally, the pannier with shoulder strap option isn't very appealing to me. When riding in the rain or snow, panniers get their share of crud splashed on them. A wet and grimy pannier isn't something I want to swing over my shoulder.

If you want to carry something on your bike, I like the idea of throwing a backpack in a crate or something protected from road spray.

I prefer not to carry the load on the bike itself for my commute. Plenty of people would rather not carry the weight on their person. It's all good.