Yet another GSSR help question

From the looks of it, Rider/Assassin/Lancer will all be good for you. I personally recommend Assassin since Kintoki is good enough as a rider and there are better lancers than what the GSSR has to offer, but it's really up to you.

You already have Waver and Tamamo, so the easy answer is Rider. It has hands down the best pool of servants: Ozy, Quetz, Drake. Only odd man out is Medb, but 3/4 is still pretty good odds. Plus I'd say Medb is still cute and niche enough to not be a terrible prize either.

Berzerker would also work fantastically. Either you get Nightingale or Cu Alter for your Buster meme dreams or you get Uncle Vlad to pair with your Tamamo.

Skip Caster and Saber for obvious reasons.

Archer is dicey as well. Tesla is great, but Arjuna and Orion are kinda meh.

Lancer is okay. Plus it's a good chance to get Lancer Artoria if you like her.

Assassin is a toss up between Jack and Jeanne. If you don't mind getting either of them, go for it. Otherwise I'd avoid it. Especially if you plan on rolling for King Hassan.

Saber: You are overloaded in this department
Archer: Chloe is good enough and apart from Tesla, the archers aren't that good
Lancer: An ok banner but the others are better
Rider: Very good choice
Caster: Obviously no
Assassin + Extra: Scathach and Carmilla can manage your assassin needs
Berserker: Not a bad choice for you. You have Waver and Tamamo, who Vlad needs to function. Cu Alter is Cu Alter, no need to explain more. Nightingale is serviceable with your lineup.

In summary, 1st) Berserkers, 2nd) Riders, 3rd) Lancers