At our level of play your only important task in the opening is to reach a middle-game position in which you feel comfortable and confident. Whatever sequence of initial moves gets you there, is the best opening for you.
For me, that's:
As White: usually 1.e4 heading into the Ruy Lopez. Often 1. Nf3 instead, heading into a King's Indian Attack.
Black against 1. e4: Sicilian Najdorf.
Black against 1. d4: King's Indian Defense, Panno variation if the option presents itself.
I choose my openings so that I can be confident of reaching an unbalanced position, where both players have strengths and weaknesses and both sides can play for a win.
I think the answer to the question "what is the best opening" is very easy, but very hard to actually resolve.
It depends upon YOU. Mainly:
1. What is your playstyle ?
2. What is your goal ?
That means, everyone has different preferences.
But for masters I think the answer is easy: they need to be prepared for anything.