Chizuru is godtier, she's basically a much stronger Lasswell (she has 120 ATK base at L80, compared to Lasswell's 96) who gets Blade Bash (Firion's paralyze attack) and Barrage when capped at 5*, and then she gets even stronger at 6*. She looks to be easily the best 5* unit in the game currently. Huge downside though: you can only get her at 4-5*, so even with a rate-up getting her is a bitch. Without a rate-up... good luck with that. So far it does not seem like we will get a rate-up to go with their release.
The other two are pretty shitty, with no 6* upgrade in sight for either.
In terms of energy/rewards, did anyone figure out yet whats best?
In terms of awakening, the 10 or 15 one ?
(And I guess, same for XP, maybe worldmap competes here too?).
Dungeons: Lanzelt Highlands - Summit is best rank XP. You'll probably want to choose which to do based on what mats you need for awakenings though.
Explores: Any 2* esper fight is best for Rank XP. Lanzelt Ruins is best for a mix of everything (Rank XP, unit XP, gil, fire/ice megacrysts, awakening mats). For Hero's Rings, if you're in a hurry to get 10 of each megacryst, do Wolfsfang Peak and Zadehl Westersand.
Vortex
Awakening: INT if you need Sacred Crystals. ADV if you need Holy Crystals. All the other mats are much easier to get on island 2, for less energy.
Experience: Always ADV.
Gil: When you get to the point where you don't give a shit about anything else, do 3 BGN a day for the daily quest. Cost 15 Energy, and you get 15 back from the daily.
Final Fantasy Brave Exvius Wikiinfo on where to go to farm specific stuff, and pretty much everything else you might want to know about the current content.