Who to Raise

I mean if materials are of no consequence, level them all, otherwise Cas-Gil, Ranma and Helena are pretty solid picks. Ideally I think every 4* and 5* is worth maxing at some point, but thats just my personal feeling.

Cas Gil is best arts crit support, ever. I would call him 4* crit Tamamo. Absolute start with him. But be sure to level his skills, they are great, but not felt in lower levels...max him before anyone else.

Fran work similar to Zerckalot, but trade crits for a much better NP gain, chance of stun+def down 1 enemy, and horribad demerit on NP. If you want another Zerc who makes stars with NP, and can work around her demerit...she's good.

Tama Cat is a poor version of Fran, later on, with buffs on curse and morph she becomes more tanky, still, leave a alone for now.

Rama,Eli-chan
Both ST Buster Sabers; Rama has crit potential, but your Liz is likely NP5; you have Musashi, bro, inferior Saber ST Bustering is probably not in your interest, yet you can use them as budge Musashi sometimes. Plus, they have more arts cards, more consistency in NP gain...

Vlad Lancer.
Quality servant, all his skills have the same cooldown, so you can Innocent Monster A+Protection of the Faith to tank a attack with the def up+taunt, or Tactics+Protection of the Faith for a really strong NP against Evil trait bosses. And the NP pierces invulnerability (which includes evades), ver good. Would say second best lancer 4*, right after Lalter.

Medusa Lancer.
Ana is overall weak, but at least her 80%+ chance of stun + up to 90% charm on males makes her a good stall unit against male archers. 1 time invuln with gutts included, kinda hard to kill. She has poor NP gain, sadly. Cu/Proto-Cu is overall a better ST quick lancer. Sadly, cuz I loved her in the plot...

Fionn.
Right now he is Stheno of Lancers, his only utility is being the only arts AOE Lancer. Later on, Claivoyance Beauty will give AOE stargen up (nothing on Casgil level, mind you...), and much way later they will reduce by 3 that pornographic cooldown of his chanced evade, also making it a 20-30% NP self-charge skill. Then, he becomes an aceptable farmer and a almost okay semi-support for arts teams.

Astolfo
Trash, aside from the future 30-50% NP charge, who makes him/her/it a good fast farmer. Raise Medusa/Marie instead, if you wanna AOe quick Riders.

Martha
Poor dmg, AOE debuff clease, buff removal+def down on strenght quest. NP hit like a wet noodle, but at least also causes def down. Caster deck, can ease you riders arts chains, plus is a godsent against specifically harsh enemies who pile multiple buffs and debuffs. And with divine banquet and the right party decks you can even stack multiple def downs from her NP, not so bad.

Marie
Protection from Arrows with invuln instead of evade, and a 5 turns small heal. NP is AOE and heals. Has another heal skill. Clearly meant for stalling. Put a Maid in Halloween CE on her, and she's unkillable.

Helena
Good support skills with horrible cooldowns; do level her 3rd skill first, as mini-AOE projection 3 turns is amazing. If you dont have Waver, 1st skill is handy.

Kiritsugu
Arts ST assassin with shit NP-gain, and excellent stargen, if you have Shki NP5, his only utility is the targettable evade.