spiral The USB Accessories feature that will be going away in favor of the USB-C port security setting was not as thorough. It covered USB acessories. It didn't cover screens / DP alt mode, for example. This implementation is also much lower level and therefore gets rid of a ton more attack surface than the previous one. I'm making sure to stress this to explain that the USB accessories setting and this new setting are not interchangable, and that the implementations and things they cover differ greatly.
That said, for the vast majority of people, option 2 or 3 (as per the numbers I used above) are likely what they want. 2 if they want to be able to connect screens etc. when in BFU, or 3 if not.
One difference here is this:
Let's say you use the 3rd option (charging-only when locked). When the device is locked, you plug in your USB-C headphones. That won't work, of course, because the phone is locked, so the port isn't accepting it. The difference is that if you unlock the device, the USB-C headphones will register. You don't need to unplug and replug in this scenario.