Oh yeah, and something that should definitely be mentioned is the freebie rare blades.

>Wulfric
Best deal you can get in terms of availability and usefulness, very good DPS blade and even gets common field skills. Use him, right now.
>Roc
No. Sure, he is available early enough but with his affinity chart requiring to raise your merc level and not actually coming with anything noticeable outside of one Smash art, he should be benched asap.
>Praxis&Theory
Praxis would have been amazing if it wasn't for 1 hit specials and 1 aux core slot. Well, lance is a good weapon and she is strong for main game enemies anyway. Theory is better imo because she offers survivability on top of actually some decent damage, especially coming from her lv3 special.
>Aegaeon
He does his job. Do use him if you want a katana. Doesn't really have anything too unique going for it, but the weapon class is good.
>Kasandra
She can gain aggro, she can keep it, you get more health just by having her equipped, there was absolutely an attempt to make her good, unfortunately the weapon class is just too limited.
>Sheba
Ok. Usable if you are willing to play with a party of mostly girls, not exactly a bad requirement since most of the good blades are female and Ether Cannon is cool on Nia, but if you ask me she isn't worth it. Also falls off miserably in endgame, muh 1hit specials.
>Vess
Lol
>Herald
Using her normally is difficult, but there is one very broken strat involving her special bullet animations and chain attacks. Look that up, it's very strong and doesn't fall off until challenge mode.

DLC ones
>Crossette
This is NOT a healer blade, she is your main DPS. Gather those potions, do them fusion combos properly, delete enemies.
What else is there to say? She is good, too good in fact. Also too cute.
>Corvin
At this point you aren't even playing the game anymore. The evasion art is spammable and makes you invincible, and his personal damage is also good. And he gets to purge rage. Holy fuck dude.