Here's what it looks like: http://i66.tinypic.com/288twkz.png

The best formation for this team is still a modified narrow 4-4-2 with a diamond in the center of the park. Mourinho has deployed it before at Inter Milan and Porto. I made a thread about this several weeks ago: https://www.reddit.com/r/reddevils/comments/592wf4/mourinho_needs_to_change_tactics_like_conte_did/

It's not just about a formation and a set of numbers by the way. It's about putting players in the positions they are best in a complementary manner. Maximizing players' strengths and minimizing their weaknesses.

The formation does not have wingers, but that is not a problem because this team does not have good natural wingers anyway. Rashford and Martial both have a strikers mentality and Mata/Mkhitaryan have more of an attacking midfielder mentality. So why not find a formation that allows players to fit into their positions correctly?

This formation allows our fullbacks freedom to get forward and whip in crosses without interfering with wingers. Pogba gets the creative freedom he needs as a LCM to go out wide and whip in a cross or come inside and get in behind to create chances. Mkhitaryan and Mata can alternate as our primary playmakers. Then you play one of Zlatan/Rooney with one of Martial/Rashford with the former playing as more of a false 9 or second striker while Martial and Rashford get in behind looking for goals or attack defenses on the ball. This would also help eliminate the issue of Zlatan's lack of pace preventing us from launching quick counter attacks when we decide to go more defensive to hold a lead (like against Everton) while also not leaving the less strong Rashford or Martial isolated up top and unable to play effectively as target men and hold up play earlier in the match. Also in terms of long-term thinking, if Griezmann is part of the plan going forwards, he works superbly with a partner at striker and Pogba is also used to playing with two strikers ahead of him as well at Juve.

The RCMs job is primarily to win the ball and distribute it to another attacker with the DM acting as a deep lying playmaker. You can absolutely dominate the center of the park with this formation.

Valencia is already regularly getting into attacking positions and tracking back effectively on the right anyway so this would not present a problem in that regard, Shaw on form can do the same although maybe we will need to get a better left-back in this case. It also allows the team to quickly organize in defense and get compact like Jose likes.

You don't have players out of position, you can play fluid attacking football with nobody having to do things they are not comfortable with or skilled in. This is the formation we should play. Not 4-2-3-1 or even 4-3-3 (although the 4-3-3 is somewhat better). 4-2-3-1 requires two very strong holding midfielders, one who is more of a ball winner and one deep lying playmaker, we do not have that. It also requires proper wingers to dictate play out wide which we also lack.

And I know people are going to say this is not the United way, again because of the lack of wingers, but Ferguson himself has actually opted for this formation in the past, experimenting with it early on in his last season with tremendous results (it also allowed him to fit Rooney, Welbeck, Kagawa, Carrick and Cleverly all into the same XI). He didn't stick with it, I believe, because the adjustment tactical shift might've hurt his chances at a title in his last year. There's a pretty good article explaining it from zonal marking here: http://www.zonalmarking.net/2012/10/08/newcastle-0-3-manchester-united-fergusons-diamond-forces-newcastle-to-change-shape/