Firstly your right that many peoples opinion will differ with accordance to there own success! as in yourself previously!, Im on level 8 but have set up my squad to play the same formation for the last 7 seasons, I have won every league since playing this!, I play 3-1-4-2 (DL,DC,DR,DMC,ML,MC,MC,MR,ST,ST). There are many reasons behind this and here is a few!, 1 you have two wide players on both flanks!, 2, The 3 defenders are backed up by a DMC for extra cover but can be used as an attacking player with forward arrows on.3 A four man midfield to act as a shield for the defence and a great formation to supporting the strikers!. 4 Having the ML,MR is a must, they provide the width down the flanks going forward and supply the ammunition to the strikers!, they also link up well with the flank defence players!.5 Two strikers up front!, I think this is a must as I find I always seem to score with at least 2 up front, plus it means you have two players in and around the box all the time.
6 When you now look at the formation on a whole it looks very balanced over all.
7 This formation can be turned into several others during or before live matches without going and buying new players!.
8 If you are losing or not playing well then you can take off the DMC or 1 MC and put on a third ST for some extra fire power so your formation will look like this..DL,DC,DR,ML,MC,MR,ST,ST,ST or DL,DC,DR,DMC.ML,MC,MR,ST,ST,ST.
9 If you winning and want to tighten up the defence then you take off a ST or MC and put on a DC! so you are now playing DL,DC,DC,DR DMC,ML,MC,MC,MR,ST or DL,DC,DC,DR,DMC,ML,MC,MR, ST,ST!, you still have managed to maintain a balanced and still effective attacking team!.
10, you can swap the 3-1-4-2 for a simular 4-1-3-2 at the start! giving you a more defencive starting line up! both these formations are near equal in strength so its your choice!.
11 You need to use all 22 players
12 Must have at least 2 players in every position so in effect you have 2 teams!.
13 You must have near equal quality players in you first team.
14 Buy left footed players for left positions and right footed players for right positions( if you can get an either foot that is better!)
15 Arrows!!!, Blue or no arrows on all defence , RED,BLUE OR NONE on the DMC, RED ARROWS on all midfield and strikers!.
16 Decide what you want to do in winning things! personally I only want the league because thats where the most revenue is won!, CL,CUPS are a bonus!, if you want to do the same then keep your best 11 for playing league matches only! and play your second 11 for the CL/CUP matches!.
17 Try to get to at least the group stages of the CL so you get some extra cash!, you may play a stronger team in the first 2 days of the season when the league has not started!.
18,, NO training before matches! only after the last game of the day!!
19 Check when your next day game is if your playing a late game that day!, if your next day/game is only a few hours away then dont train that day!.
20 try to keep upgrading every player position as ofton as needed!, try to have the youguest squad you can afford.
21 Special abilities , defencive wall for DC....ariel defender for DL,DR....dribbler or corner specialist for ML,MR....play maker or free kick specialist for MC.... one on one, penalty kick specialist for ST.

These are only my tactics so its only a guide! hope it helps.

If your defense sucks more than you can take, you need to play DL-DC-DC-DR. 4 at the back make a good defense.
If your defense is ok, play with 3 DC's.

Personally I play most of my games with 3DC narrow but I got a quality defense line. For me the important thing is to control/dominate game and because of this, I play with 5 in the middle field. Finally I choose 2 strikers for most of the games.

Since you want to play with you AMR, I will give you 2 options: Either go for 4-4(ML with red arrow+MC+MC+AMR)-2 or 3-5(ML with red arrow+MC+MC+MC+AMR)-2.

If you like my suggestion I strongly suggest you find the best ML/AML you can get and play V-style (3-5-2 or 4-5-1) or even more daring 3N-3MC-AML&AMR-2.

I HOPE THIS WILL HELP YOU..

please comment and give me some idea for the best formation..