The knight Attack (aka fried liver) for white
Nimzo Indian for Black
Best for what? For solid play? For dynamic positional play? For sharp play? For creating imbalanced positions?
Personal preference?
King's Indian Attack as White.
King's Indian Defense as Black against 1. d4.
Sicilian Najdorf as Black against 1. e4.
In terms of personal preference, for White it's Grunfeld exchange variation, for Black it's QGD Tartakower and the Panov-Botvinnik in the Caro. I find the play from either side to be interesting.
Just kidding.
Standard, classical openings like the Spanish, Italian, Queen’s Gambit, … are the best.
On the Youtube video "Opera Euro Rapid | Qualifications jour 1 avec MVL et Magnus Carlsen" we can see strong GMs playing in 15m+ (...) s (by searching we should find a video of the same tournament in English language) and to the first round Alexander Grischuk made a keystroke mistake against Anish Giri which gave as position 1) e4 e5 2) Nf3 Nc6 3) Bb5 Nf6 4) Kf1 :
And at the end of the game Grischuk still makes a draw.
So in short this to say that according to me even if the opening has or can have a rather strong psychological impact, the chess game is too difficult or complicated to be mastered (even super calculator being able to calculate at least 3 million of positions per second do not manage to do it and it is simply impossible that a human can produce a similar calculation performance) which means that there are plenty of good enough or not bad enough openings that can be ok and that defeat or victory is not really in the opening (except tactical error or quite concrete error in the moves of the phase of the beginning of the game).
So in the end I don't know just there are opening mistakes leading to losing positions or garbage openings (that don't necessarily lose but that we don't wish to play) I can decide to say that they are not the best then there are the "real" gambit openings I won't put in the best.