Any tactical idea for using 4-2mc-2W-2st?There is no best formation as this varies from situation to situation, and also this depends on what is the most used formation and tactics among opponents in a particular batch.
For instance, if you are in a league, where say more than 50% of the opposing teams use a common formation, and the formation you usually use is among the ones that counters this particular formation, you will likely to say that the formation you used is the best formation. But, then what if the next season, you are put in a league where 50% of the opposing teams usually use a formation that counters your usually used formation? Does that make your formation be among the worst? No. Many of the replies here might be biased due to past experiences (what worked for them) and/or preference in style of play.
But, it is possible to classify some formations according to which generally works (including which formation counters the most formations), which cost less to use and so on.
4-1-2-1-2 N.D and 4-3N-3N can be classified as good attacking formations. They are also relatively low on cost, though 4-3(N)-3(N) is even more cheaper to use, and is also less predictable.
4-5-1-(V) is a very good counter-attacking formation. While some people may say that this formation is flexible, it is in fact limited, and it is predictable (I won't say how so as not to disclose things that may affect some users positively or negatively. That is up to you to find out.). It is also a formation that costs a lot to use and maintain. AMLs and AMRs, especially the good ones or the right ones, are more difficult to find on the market as compared to MCs And STs, though this might vary from server to server.
It seems that 4-4-2 is a good formation too. But, MLs and MRs might be more difficult to find as compared to MCs.
I would classify those 4 formations mentioned above as more appropriate for debutants and lower-intermediates. Once a user gets to know the basics of those formations, he is likely to win some competitions by using one or two of them (in fact, some have won a lot using mostly those formations).
3N-2W-2N-2W-1 (Butterfly) is an expensive formation to use as in addition to AMLs and AMRs, there is the need for DMLs and DMRs.