Hard to split them! Benji's defense has dramatically improved this year which has seen him contribute not only in attacking plays but also in defense. Benji also adds a lot of creativity and attacking flare to the way the team plays, this season Benji make less low percentage plays compared to the last few season.
While Farah who doesn't seem to get as much publicity as Benji, contributed just as much or in some cases more to the team. Not only in terms of his work rate per game, but also as a leader and mentor to the younger players. I also thing he was more consistent than Benji, except maybe during the finals series where some of his plays didn't pull off. The frustration showed.
They both helped the team get to the finals this season, they complement each other in lots of ways which helped create the complete skill sets needed for the team.