Which combination of minor pieces?

2 bishops is usually better than bishop and knight / 2 knights, but which one is better between bishop + knight and 2 knights?

Winning with 2 knights is not possible, unless your opponent is making inaccurate moves by moving his King in the corner. If King stays in the middle of the board or around it, you will not be able to checkmate.

First of all, the thread is about the middlegame value of pieces, not about mating a lone king.

Second, in the endgame of 2 knights vs a lone king, you can't stay in the middle of the board. The knights player can push you to a corner. But at that point there is no way to force the checkmate.

Position dependant  Open = With bishop

Closed or semiclosed = With knights

Generally
BB > BN > NN
The bishop dominates the knight as it covers more squares.
Two bishops complement each other, two knights are redundant.
Of course there are exceptions, where N>B, N>R, or even N>Q.