Id choose a 4231 formation :
=================De Gea ======================
Rafael======Smalling/Jones======Vidic/Evans====Evra
==========Cleverley=======Carrick=================
======hazard=====rooney======kagawa===========
===============welbeck========================
this formation with a fluid front 4 that keeps interchanging their position. therefore on another day, rooney could be in Welbecks place, kagawa in the middle, and either young or nani on the side with hazard. Hence no need to buy new strikers, even if berba goes. the players there would have to play close to each other, not like we played this season. This would benefit quick passing for kagawa, welbeck, rooney and clevs. fullbacks to provide the width. We would also have to change the way we defend. carrick would act as the shield in front of the defence, cleverley as a box to box and we will have to defend high up on the pitch. i.e when loosing the ball, instead of dropping deep, pressure the opponent to get the ball a la barca. one important thing is that valencia and chicharito wouldnt fit this formation, theyd be used as plan B when we revert to a 4411/442 when we cant score.
Or a 4-3-3 formation
=================De Gea ======================
Rafael======Smalling/Jones======Vidic/Evans====Evra
======================Carrick=================
===========cleverley===========kagawa===========
=======hazard=========rooney===========welbeck============
Using the same tactics. The only thing i hope is that, if kagawa is coming, hazard would just be a bonus, and i hope he'll play the CAM/LAM role. and i could see him combining well with cleverley, welbeck and rooney. He reminds me of iniesta in his way of always looking around him when he doesnt have the ball to know where his team mates are and always seek for the pass and move. hazard for me would just be a bonus, but that would mean nani and young having less time to play, and if we use a fluid formation, valencia would have even less time.