Guys I need help,
SSRs:
Saber - Mordred NP3, Altria
Archer - Orion, Ishtar
Lancer - Brynhild
Caster - Tamamo, Merlin
Rider - Medb
Assassin -
Berserker - Vlad III
I'm debating whether to roll on the Caster banner for Waver in order to break the game, or roll on the Assassin Banner for an SSR that I don't have, OR try and roll for Cu Alter. I'm honestly not too pressed for assassins since I have Scathach, Shiki, and Carmilla, but Jack could be a nice addition.
I'm pretty risk averse from personal experience so I'd go with Assassin/extra out of the ones you listed, but it really doesn't matter. It all comes down to luck anyway, and with your lineup you don't need any of them. I'd honestly say go rider, but since that's not one of your considerations, just do what you want.
If you don't mind Monk, I would go for Caster. Otherwise, Assassin or Rider.
I suggest Assassin banner since getting Jack is a 50% chance. Probably the best odds of ever getting Jack. No rateup/future GSSR's guarantee a 50% chance for Jack so go for that. If you do get Jeanne that's ok, because Jeanne is amazing for the upcoming late-game things. She will protect your ass.
If you plan on rolling for King Hassan (up there with Jack for the best assassin slot), then go for rider. Rider has some pretty strong contenders: Ozy, Quetz, Drake. You probably can get np2 medb but its up to RNG and this could apply to any other banner as well. Riders/Lancers have the strongest units but since you have Bryn who is pretty good I suggest you roll Rider.
TLDR: Go for Jack if you arent rolling on King Hassan. If you are rolling on King Hassan, go for Rider/Lancer. Preferably rider. OR you could just pick a banner that has your favorite servant(s).
Assassin/Extra, you don't have either. It's good to have coverage for anything DW throws at you, you never know when an assassin or ruler will come in handy.
Based on your servants rider would be best to roll on imo.There is a good chance you will get a excellent rider.Hopefully you can get ozy or quetz
