MROD, try not to worry about LOOKS and go with what feels good to you. You are all the matters, and frankly, I have never thought, when I looked at somebody with a handbag, that it would look better carried one way or the other. And how is the casual observer supposed to know whether a bag came with a shoulder strap or no?
SO you are overanalyzing this.
i like the long strap left on, even when i'm not using it, it means i always have the option to use it if need be, like if i need two hands for something i just stick it on my shoulder. i sometimes leave it dangling or sometimes pick the middle of it up and hold with with the short handle, i have no rules, just whatever feels comfortable but i never take the long strap off, it's too convenient to have it on