The Riding though that castor reminded me of is good. Something to actually trigger he super effective modifier.
Saber Lily: leveled to 60 for Saber Wars and never touched again
Liz Brave: never leveled
Nobunaga: maxed, used until I got Rama and NP2 Tesla
Kuro: maxed, use sometimes
Santa Jeanne: never leveled
Santa Alter: never leveled
Kintoki: never leveled
Caster Liz: maxed, max skilled, key staple or early game team
Irisviel, maxed, only used against Goetia
Shiki: maxed, maxed skilled, go-to Assassin until I bond-maxed Tamamo and Waver, key member of Arts team
Scathach: never leveled
I either used event Servants that filled holes in my roster (Shiki, CasEliza, Kuro) or I really liked them (Nobu).