But I prefer my beginnings to "hit the ground running". For example, in the follow up to From Light to Dark and Back Again, this start comes from a story called Time for Some Peace.
The noise was becoming unbearable and getting nearer.
I like beginnings that intrigue, draw you in and make you want to know more. I want the end of the story to make me feel as if I've found out what led to that opening line being written the way it was and that it was worth finding out. I have no problems at all with stories "just" being for entertainment (what on earth is wrong with that? Not all stories have to have a particular message). I also love twists in the tale (and sometimes the twist can be there isn't one!).
So once upon a time is a great beginning but unlikely to be one I'll use!