Should I keep Elizabeth caster or should i roll for Nero Caster?

Nero Caster looks pretty good from what I see of her skills on this site... but unless you're a whale there's no way to know if you'd get her. And especially if you have Liz at NP5, I don't see why not level her up in the meantime. I haven't used her a lot yet, but she's OK at simple farming. I can't say how she'd be at farming anything hard.

Nero, because.....

(1) She has 2 normal Buster card, which could be more beneficial by Merlin's 3rd skill, no matter critical Buster damage, or NP-x-B brave chain. Let along SSR has higher attack status that SR.
(2) She has way better NP side effect (Ignores Invincibility, very good since many assassins have evade and invincible skills) and OC effect (20%-60%, NP damage, should I explain that too much?).
Liz's NP's side effect (ignore defense) is good, but her OC effect (curse) also almost useless in most cases.
(3) Her attack-up buff is really strong, combined with 1 Merlin could reach +100%.
(4) 1st skill make it work way easily for NP shooting particularly if you dont have Waver. Even the 6 turn cooldown can be one best np-charge skill.
(5) She has excellent NP gain, although 1 less art cards. Further with her 1st skill, she can make NP spam very easily. Therefore even though Liz is NP 5, Nero can still easily deal much more damage than Liz.
(6) Her 2nd skill make her stand longer which could be beneficial in a multi-class enemy fight.
(7) Better team can make Nero better, like pair with Merlin+Caster Gil will make Nero good got both NP spam and critical damage (even work like a star generator). Also her bride saber can make her excellent.

Liz is indeed good as farming AOE servants, but somehow not excellent as Nero.

Casliz is good cuz she is free. Of course casnero is better.