Lacking in Lancer which banner should I roll?

Altria lancer is a pretty strong AoE damager, tamamo is good but she has demerit on two of her skills i guess

Liz functions as a decent wave clearer for dailies and such. Altria Lancer is a stronger version of that, so I don’t think that would be the one I’d aim for if I were you. A lot of it depends on what your team build is. I use Scathach for Crit and Shuwen can do massive single target damage in an Arts team.

Tamamo lancer will serve well as a Crit Damage dealer if you have the teammates to support that set up. She is also more focused on buffing and damaging male servants so you have to think of your team comp there. She will certainly be a great servant in a Buster Crit team and is a ST Np which is nice since you already have Liz for AOE. If she fits your team comp, you’ll definitely want her. I just personally feel Altria Lancer just fills the same roll as Liz, just better at it.