Fullbacks
Nathaniel Clyne & Alberto Moreno (2015) v Trent Alexander-Arnold & Andy Robertson (2019)
Clyne was one of those players that stood out during that season and was arguably the most reliable Liverpool player. On the other hand, Moreno was, to put it lightly, disappointing. He looked decent while attacking but was equally poor while defending. Wingers ran rings around him and like Mignolet never looked trustworthy. Although he showed improvement in the start of the 2017/18 season, he got injured and was replaced by the new signing, Robertson.
Alexander-Arnold and Robertson have earned the tag of the top two full-back pairings in the league and Robertson is being touted as the best left-back in world football. They love to bomb down the wing to provide width but at the same time pay full attention to their defensive duties.
At the moment it would not be fair to say that Clyne deserved to be replaced by a new right-back, if not for injury. However, in the Robertson-Moreno comparison, the Scotland captain wins by a massive margin.