Defensive/holding midfielders
This seems like a straightforward call for Unai Emery this season. His most effective duo in midfield has to be the combination of Granit Xhaka and Lucas Torreira.
The Uruguayan's hard-tackling, badger-like closing down of opponents in midfield gives this midfield the edge it needs, especially when playing against sides who like to keep possession of the ball for long spells. Torreira was Arsenal's leading tackler last season and only second to Shkodran Mustafi in terms of interceptions.
The second half of this double pivot, Xhaka was the pass master at Arsenal last season with a large chunk of the play going through him. The Swiss international has a well-rounded style of play that sees him make plenty of tackles and interceptions, aiding the side not only in attack but defence as well. He was only surpassed by two Arsenal centre-backs (Mustafi and Sokratis) for aerial battles won as well, which is an added security in defence.
Matteo Guendouzi and Mohamed Elneny are good deputies to have for Emery with a slightly different skill-set allowing the Spanish coach to tinker based on the opposition. The likely incoming Spanish midfielder Dani Ceballos could also play in this double pivot when Arsenal are chasing a game or facing a low block, but more on that later.
The biggest worry Emery will have is the inconsistency in this area. Both Xhaka and Guendouzi tend to blow hot and cold in games and will have to improve upon that if Arsenal have to make any discernible progress from last season.