If there was a "best" opening, it would be the only opening.
Asking which opening is "best" leads to more questions than answers. Namely, "best for what?"
What do you want from an opening? Wild kingside bumrush? Open tactical melee? Closed positional grind? Rock solid defense? Ability to trade down to a positive endgame?
There are many openings to choose from for each thing you are looking for. Of course, each opening has its minuses as well.
To me, chess is the most fun when I widely vary my openings. It slows down my development at first, but I feel it's best in the long run; and since, like I said, I'm having fun, that's not an issue to me :) I fully expect to nail down a bunch of openings in quick succession one day because I'll have at least a basic to moderate understanding of so many of them.
As for my favorites, though? Probably the Ruy Lopez or Reti for white and the Alekhine Defense for black. I also like the following opening for both sides, but I can't remember its name:
1. d4 Nf6 2. Nf3 g6 3. c4 Bg7
^ That opening leads to some really fun games IMO.