Marie is useless and will stay so until we get the sailor boost that happened in the DMM version.
Rowanna is a good duelist, although she can be tricky to use. (You have to let her health go somewhat down, but at the same time she won't live long without healers) She is the only free unit with a resistance to debuffs (poison, paralysis, desert heat) after awakening, which makes her much more useful.
Shiho is a really versatile unit. She has a decent damage output and her faster attack speed also increases the speed of her healing, making her a very proficient healer.
Rika cannot be healed and during skill activation (with AW'd skill) she can do ranged true damage. She also has quite formidable stats to make up for the fact that she cannot healed. She can be good if you need some support against a boss. And her AW'd skill makes her one of the best event units.
Lynn & Ada: Both are decent, but you can do without them, so don't prioritise them over others.
Horace is the better of the two event magic fencers, but that class is quite niche and situational, so probably shouldn't be a high priority.
Beatrice: Bleh, useless. Her skill takes away the only reason why you would ever use a pirate: her range. It shortens the range so badly, that she almost becomes melee.
Momiji: Again, useless. Her skill looks good but the short active time, the paralysation afterwards and the fact that her AW slows her attack speed makes it borderline useless. If you have Liana to negate her paralysis after skill use, then she is somewhat useable, but meh.
Azami: Get Saki from the TP and use your Azamis to level her skill. Maybe leave a copy, just in case if her AW'd skill makes her useful (it's not yet implemented even on DMM as far as I know), but as is, she is useless compared to Saki. Which is a shame because I really like her.
Claudia is the only free event unit that can do true damage pre-AW and she is a death sentence to dragons and dragonkin later. She is one of the most useful characters on your list.
