I think most likely I'm going for the assassin/extra but I would like your opinion as well.
My lineup
Saber: Brave Liz, Rama
Archer: Emiya
Lancer: Santa Jeanne, Liz, Vlad
Caster: Merlin, Tamamo, Helena
Rider: Santa Altria, Ozy
Assassin: Emiya
Berserker: Cu alter
Ruler: Martha
Ya i would go with the assassin/Extra class your deck seems well balanced enough as is and since jack is the only 5* ever on the GSSR and doesn't get to many rate ups. So if you need a better assassin or want jeanne then i would highly suggest the assassin/extra banner.
assassin/extra seems fine considering your line up.
Since you have Merlin you could also take a look at the lancer banner.
