The formation I tend to use all the time is a 4-1-2-3. I have a back four all set to CB with the 'full backs' nudged up a notch. Then put on CMF at the bottom of the centre circle in your own half.
I then put two wide AMF as far up and wide as the midfield section goes. I the put an SS in the 18 yard semi-circle and slightly to the right. An SS to the left of the penalty spot in line with the goal post and a CF all the way up and against the right post.
This formation works amazingly as you have at least 5 defending all the time and 5 attacking, 6, 7 or even 8 if the CMF and full backs have time to join in. The pushed up CF and SS's also push the opposition defence back leaving a hole for the SS on the edge of the box and the AMF's.
I find this formation awesome because it allows me to play down the wings and bang loads of crosses in during a game with 3 strikers in the box waiting to receive, strikers and AMF's are high enough up the pitch to create problems when playing long ball over the top and the hole created between the opposition defence and midfield due to high up strikers allows space for a passing game to split the defence so it suits most styles and i usually get 15 odd minimum shots in a game.
Then, if you want to defend your lead, you drop the CMF to DMF and bring the lowest SS back to AMF (or substitute and put in a second DMF to protect defence) and drop the AMF's to RMF and LMF to protect a lead. If chasing the game, nudge the CMF up to the halfway line and one, or both AMF's up to RWF/LWF.
This works amazingly with teams like Man Utd but I also use Sampdoria and Blackburn regularly using this and compete against teams like Barcelona, Inter, Utd etc.
It should look like this:
- - - - - - - - - - GK - - - - - - - - - -
- - - - - - CB - - - - - - CB - - - - - -
- - CB - - - - - - - - - - - - - - CB - -
- - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - CMF - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - -
- AMF - - - - - - - - - - - - - - - AMF -
- - - - - - - - - - - SS - - - - - - - - - -
- - - - - - - - - - - - - - SS - - - - - - -
- - - - - - - - - CF - - - - - - - - - - - -