Just 
say “regarding!”
Is there some nuance?
Yes.
Are there variations of meaning that would necessitate different usages in specific contexts?
Also, yes.
Are you in any of those situations that require that level of nuance?
99% of the time, no – no, you are not.
Just say “regarding.” It will cover the vast majority of your usage, and you won’t come across as pretentious. It’s a total win-win, right?