Bluetooth is slower and generally feels a whole lot more klunkier. It's also not scriptable, whereas I can write an easy shell script to scp or ssh something to another box using the keys to authenticate.

By the by, Bluetooth is a whole lot less secure if someone nefarious is within range.

Using https and gmail is too awkward and out-of-the-way.

USB only makes sense if you're connecting to a PC to access the SD cards--which may or may not serve your purpose. If you're trying to simply read/write the media cards, this is fine. If you're trying to script some cross-server automation or some file transfers to the /home/user path, this will be insufficient.

Using the SD card is, again, only appropriate if the whole point is to simply move files over to the SD card. Then there's the whole argument of wear and tear on the kickstand and the SD card's door.

I personally prefer to use ssh and scp to access and to transfer files. On rare occasion I will use bluetooth. I prefer not to use wires as much as possible and see very little reason to put any more wear and tear on my device by doing so.