I agree with transpo.

Generally kingside, but queenside can offer some interesting attacking possibilities. However, you will need to use some time to get your king to a8.

As an experienced caro cann player the rule of the tumb should be to castle the same side that white does. Caro Cann might seem like a bunker but with oposite castling white is often faster (ofcourse there are some lovely exceptions in that such as the game tal vs pertrosian).

Ofcourse  castling the same side might run into tacticle probloms specialy round f7 if you blindly follow your oponent and catle long.

And yet Shankland's own video series on the subject supports opposite side castling as the 'rule of thumb' with same side only being in certain situations. Care to explain the differing of views there?

Great game last week between Kamsky and Seirawan where Seirawan played the Spassky variation, castled on opposite sides and got murdered by a viscious attack down the g-file.

DD