I played with an opponent for quarter finals in cup, slightly weaker than me. He used this 4-1-1-3-1 formation, so I got my usual 4-5-1 V formation (normal mentality/wing focus/mixed passing/no counterattacks/normal pressing/soft tackling/zonal marking/offside traps). By 14' I was losing 0-2, and by the end of the first half, I was losing 0-3!
In the second half, I changed to defensive mentality, long passes, counterattacks, hard pressing and normal to hard tackling. The final result of the 1st leg was 3-3!!! 2nd leg I started with the changed tactics I mentioned before, and I won 1-2, without watching the match!
So in my conclusion:
i) selecting formations should be based on the opponent's formation (and your players of course)
ii) selecting tactics should be based on the opponent's quality (and the specific match of course).