Suggest the best move in this position

I was playing as black and blundered by moving my bishop to g4. What would have been the best move in this position (black to move) and please explain the reason behind it.

In the analysis, it is showing that the best move was pawn to h5 but I can't understand why?

A "best" move is going to differ based on the engine, hardware, etc.  So lets skip right past that because we are humans, and we make mistakes. 

The engine probably suggests 1...h5 because white has the space advantage on the kingside, and g4 is looming.

But i also think you would be perfectly fine playing any of the following:

1...a6

1...Qc7

Its early in the game.  You could pretty much play anything and be ok.  Keep it simple.  You want your moves to do as many things as possible.  You need to complete your development.  You need to castle.  If you have no idea what to do?  Your opponent has 2 pieces on your side of the board.  How can you drive them back, or force an exchange?

H5 is because white is actually threatening to win the bishop with g4.  But bd6 or qc7 should also work, and seem like natural developing moves, so your question remains valid.  

What to do after eg. 1... Bd6 2. Nxd7 Nxd7 3. g4?

Thanks a lot KetoOn1963 and ArtNJ !