Mei and shikamaru. Lava and genius>>wind fan and byakugan. Neji will put up a tough fight but lose.
You do realize Neji has another team mate of equal footing? How does he put up a great fight alone against a kage and a chunin while Temari is completely ignored?
Temari does have great counters to acid mist and so does Neji to some extent. Not only that but why would Mei use it against her own team mate?
Mei's water style is very powerful so that will be hard to over come although a vacuum palm from Neji and a wind cast from Temari should be strong enough to overcome any and all of Mei's attacks IMO.
Still with Shikamaru's help Mei should win since I think Mei can use her various abilities to increase the length of Shikamaru's shadows. These abilities include a massive water wall or by using a mist in a small local area which will allow Shikamaru to extend his shadows.
Neji's Byakugan does give him an excellent field of vision so he can help Temari by telling her the location of Shikamaru's shadows at all times even if Mei's attacks block Temari's eyesight. Still the Byakugan does not provide a full 360 degrees vision so someone as smart as Shikamaru should be able to exploit Neji's blindspot and capture him. Also since Neji is a CQC fighter, he will have trouble approaching either Mei or Tsunade.
To do this, he will need Temari's long ranged attacks to defend Neji from Mei's attacks as well as Shikamaru's because Temari could kill Shikamaru if he is busy trying to grab Neji.
I'll go with Mei and Shikamaru high difficulty but I don't even know the starting distance, location, knowledge all of which are important in determining an outcome in a battle.