There will be those who will tell you that formations dont matter much or at all in this game and they may be right , I am not sure. I use a defence of DL , DC , DR with a DMC sitting in front mostly with occasionally a second DC if required but this is fairly rare. I have some success with my teams winning some Leagues and never outside the top 4. Other managers have more success than me but formation isnt a major reason for this , there are other things that they do that I dont or wont do and good luck to them.
I have also found that in general teams using 3 AM's with 1 ST usually score more goals than teams using 2 ST with an AMC , not a lot more but more but they also tend to concede more as well in general. I am sure some smartie will get in here and say different concerning only their team. That is the way of it in here.