ST Saber: Bedivere if you have him at NP2+. Caesar does well enough as a DPS, but he’s more a support.
AoE Saber: Fergus is your only option, really. He’s actually very strong, but can have trouble charging his NP in a team context (gorilla deck).
ST Archer: You have Robin already. But if you want someone else, Billy is great with his NP battery. While not really a DPS, you shouldn’t neglect David. Harp of Healing FTW.
AoE Archer: Touta is getting his NP upgrade soon. He has a good mix of offensive and defensive tools.
ST Lancer: Taiga hits very hard, but she’s story locked, so you may not have her at high NP level. Original Cu is an incredibly good servant, and can deal more damage than his peers over time thanks to his survavility.
AoE Lancer: Hektor and Romulus are rather comparable. I’d give the edge to Hektor since he already has his NP upgrade. Proof of Friendship is actually pretty good for harder quests.
ST Rider: Ushi, hands down.
AoE Rider: You have Medusa already. But you could raise Alex’ to support her.
ST/AoE Caster: With his upgrades, Babbage is hitting the hardes.
ST Assassin: Jing Ke for burst damage, Hundred Faces for more damage over time (NP loops).
AoE Assassin: Even though he’s a support, Kotaro is your best shot. But if you want to become a memelord with Phantom, be my guest.
ST Zerk: Lu Bu, please. His damage is disgusting.
AoE Zerk: You have Spartacus and he’s about the best for that role thanks to his NP battery. Darius and Erik are also very good, if you have the CEs supports to help them charge their bar.