GSSR Advice Please?

Lancer, caster and rider are your best options imo.

Caster because Waver. Xuanzang is pretty good too. Lancer because you don't have many good ones (though what you have is good enough, doesn't hurt to get more). Rider because you don't have any of the GSSR ons, and they are almost all good. You could use a better assassin, but Jack's banner has a 50% chance for Jeanne NP2 to spook you, and that's a waste, so not worth it imo. Same problem with zerker, unless you like Nightingale, Cu Alter is the only prize.

Given that, I'd personally recommend Rider, since 3 out of the 4 are the best (or close to the best) at what they do.

Saber : you lack AOE/Wave clearer, already strong ST.
Archer : more than enough.
Lancer : Proto Chu is a Good Crit Lancer and Jalter santa Lily is a strong AOE Lancer, enough.
Rider : more than enough.
Caster : Hans, Tamamo and Marie Caster is very good supp, more than enough and you have pretty solid supp Caster.
Assassin : enough, Scat and Emiya is a pretty strong assassin.
Berserker : there are AOE Zerker Cha-cha from the next Guda-Guda Honnoji and since you only have a single zerker, Zerker banner is a solid choice for you ( Nightingale is also a good semi-supp zerker ). The jackpot is Chu Alter if you need a very strong Cockroach zerker.

For me, i would recommend Zerker Banner ( if you aim for Cha-cha then skip GSSR Zerker banner ) and Saber banner, at least Artoria is worth raising and i recommended this one the most.

Archer: more than enough
Rider: Kintoki alone is enough
Caster: mostly support but it's enough
Assassin: enough since you can make Arts team.
Berserker: same with above.

I'd say go for Saber or Lancer. If you ask me which one is better then there's no difference. So feel free to pick whatever you want.

I second ArcZero's comment.

Why not caster banner? Waver would be great but the Chance of NP2 Tamamo is quite high.
Why not Berserker? Same as caster - Cu Alter is amazing but you already have Vlad NP2.
Why not rider? Imo Kintoki NP5 is better than all the available 5* servants at NP1. Plus, you have Santa Alter for AoE.

Between the saber and lancer banner I think the lancer one is a little bit better due to the quality of servants in it.