Defenders
Arsenal's defence for this season should ideally be: Right-back: Hector Bellerin, Centre-backs: Shkodran Mustafi and Sokratis, Left-back: Nacho Monreal.
Despite Lichsteiner's arrival, Bellerin should be the starting right back for this season. Stephan Lichsteiner came from Juventus this summer. He is 34 years old and it's hard to believe that he will be the first choice for this position. However, he will surely bring some competition and Bellerin will benefit from that. So, we can expect him to be in a very good form this season. His speed is his biggest strength and that will help a lot in Emery's transition system. Last season he scored 2 goals and provided 3 assists. Arsenal fans expect big things from him this season.
Laurent Koscielny is Arsenal's first captain and surely their best centre-back. However, he is currently injured and this is a big loss for Unai Emery. Sokratis Papastathopoulos came from Borussia Dortmund this summer. He is a decent buy for Arsenal. Sokratis is a solid defender with great experience. He was one of the best defenders in Bundesliga for most of his time at Dortmund. He also has some great leadership qualities which will help while Koscielny is out. His partner in the heart of the defence should be Mustafi. Mustafi has had a very good preseason and he deserves praise for sure. When he is on top of his game, he is Arsenal's best centre-back after Koscielny. He will surely get even better in Emery's well-structured system.
Nacho Monreal should occupy the left back position. His competition for that position is Sead Kolašinac. Emery wants his team to get the width from his attacking fullbacks and in that terms, Monreal is better than Kolašinac. He will join attack constantly and their defensive midfielder will drop deep to form a back 3. Last season Monreal was probably Arsenal's best player. He scored 5 goals and provided 2 assists in 28 matches in Premier League.