Recomendations for a healer?

Nanna is the closest thing to Elise you’re gonna get. With an Atk boon and an Atk+3 A slot or sacred seal, her attack and speed will be comparable to Elise

Lucius and Wrys can double as magic tank soakers since they have the highest res, Lucius comes with Pain+ by default so can run dazzling savageblow on top of that. Among the other cavalry, Priscilla has Rehabilitate+Panic, so can dazzling panic any enemy buffs, and Rehabilitate may be seen as the worst healing staff now but still good imo.

Clarine is good to, she has martyr+, fear+ and she's in a horse.

Just find an atk+ or spd+ IV.

If you want to have a fun crazy one; take Azama
Preferbly with a def boon.

He can dish out a lot of pain and is a great user of fortress def or res.
Just make sure to slap rehabilitate on him (or recover+ if you can afford it)

You can never go wrong with physic users. They can heal from the safety of the backline. Of the 3 that comes with physic, sakura comes with atk debuff so shes pretty good imo.

All the healers I've listed below are 5* and have eaten other 3-4* healers for skills, but not other 5*s. So I mostly run default kits. The amount of Hero Merit each of my healers has gathered should give you an idea about how useful/fun I find each of them:

Lucius: 4727
Priscilla: 4282
Lissa: 4169
Lyn: 4166
Lachesis: 3705
Serra: 2177
Maria: 1701
Nanna*: 536
Genny*: 51

*Notes below to explain low HM for Nanna and Genny.

Lucius gets my vote for most useful/fun, but I run him mostly in a specific team, and all the skills just kind of mesh perfectly with Martyr+/Pain+. I can provide more detail if you want it.

Other than that, I love rehabilitate (and prefer it to Physic), so Priscilla with Live to Serve, good movement, and horse emblem buffs takes second. Lissa takes third because recover is useful but in general too slow for running TT. Lyn's B slot is sadly occupied. She's great at taking cheap shots and preventing damage to the rest of the team. But she can't heal herself, and this makes using her a little trickier, because I need to keep her away from Pain and Savage Blow users. In a tight spot, she sometimes can't be saved from taking a little damage, which she might carry for the next several maps if the rest of the team doesn't have HP manipulating skills.

Physic is a very flexible skill, but Lachesis's main asset is actually Absorb+. Being able to get cheap shots on the opponent and heal your team at the same time is quite nice, and the healing will even happen during the enemy phase, if Lachesis is attacked. Serra was an experiment (I assumed she would be terrible, but she wasn't). Her ability to hone both attack and speed, as well as restore HP to the entire team during the enemy phase while simultaneously tanking mages, is just incredible.

Maria is so-so.

Nanna's use case is just different. You don't use her because you want a healer. You use her because you want someone to get rid of panic, gravity, and debuffs. Her HP restoration abilities are actually kind of terrible in comparison to the others I've listed. And mine is -atk (30 after weapon is equipped) which makes Restore and Absorb both weaker on her than they would be on other units.

And I literally just pulled Genny last week so I'm still building her.

EDIT: Also, I don't know when this happened, but Martyr and Rehabilitate used to have Cooldown+1. They don't any more.