Me too stuck at 4-4-2 for long time, then again why bother to play at classic, win or lose at least can experiment the tactic work or not.
If you are too afraid to lose a match, yes you should stick to one formation coz player already settle at that formation and conformable to play coz you have all round 6 or 7* player to deal with 4 or 5* player in the opponent field.
On the other hand, If you are adventurer, you should keep switching and countering opponent formation, mostly if you are under-dog to fight against the shark. you need to cover most of your half and countering if opponent player under perform. May be hope for a draw or lucky win.