In this scenario, which I continously run into while playing Scandinavian defence, I wonder which way would be best to castle, Kingside or Queenside?

I ask you some kingforking,just a detail,a opinion of yours about your opponent's move,cause this move is commonly used in many matches but I use not to intend a move like that every time:why after 5...Bg4 he forces the next one developing his H pawn instead of developing his white squared bishop to 6.e2(covering his king too)?let me know.

I guess there's a specific intention to force black bishop catching or he doesn't know how use in that situation his right knight,so let me know your opinion,thanx.(please notify me when you reply,have a good going)

I would never castle Queenside here! Your opponent has a Queenside majority, and has castled Kingside. He will attack your Queen with tempo as he advances his pawns (Like tonydal pointed out.) and quickly mount a large assault. You would never be able to mount any sort of counter-attack, and your game will degress into a loss. The best thing to do if you want to castle is to clear up both sides of the back rank and wait to see where your opponent castles. Then castle quickly on the same side. Opposite side castling is a signal for an all-out attack, while same side castling means that both Kings will be mostly safe 9Which is what you most certainly want!)

I personally learned that as the main line and a substantial amount of my opponents usually make the same move. I assume that he is simply trying to force my bishop away. It seems a little Morphy Defesenish aswell. Maybe he's trying to force a trade which I ultimately take to try to cut down white's space advantage when I play Scandinavian.

Out of curiosity, what move do you usually make instead?

if there is no need to enforce control on d5 I'd simply put my bishop on e2 checking my knight and freeing my right side to castle,I think it's a good way to earn a little advantage on myself,in my developeing,I satisfy two needs once

Kings side would be better I think in this position. But in most games I like a Queen side castle, puts the Rook on a open file.

I thiunk king side man 'cause other wise he'll just kill you with his queen