MAG/SPD Sanae
Main Tank Eirin [Abusing her ability to selfheal with Hourai Elixir, excellent elemental resists, and her naturally high HP stat. I'm thinking a self-sustaining Komachi with actual defense stats]
Mokou [Never used her]
Sakuya [I always go with Aya for speedbuffing. Always.]
MAG Sanae should be able to roughly fullheal most characters (Not the major HP ones like Meiling), and does okay random battle damage. But, really, MND with a magic buff on her for her heal works out better so she can take hits (also makes it possible for her to maybe use some miracle fruits)
I always find it impossible to not compare her to the faster, cheaper, stronger-healing, tankier Minoriko though, because you generally should not need the status/debuff cure on Sanae's Heal, and Miracle Fruits is bad since it's slow when considering there's faaar easier ways to buff up people's stats.
Mokou is okay, but underwhelming. Neither of her defensive stats are good enough to make her better then a different average non-glass attacker, and neither Fujiyama Volcano's formula nor her MAG are that great; plus the former is kind of expensive. She's fine, but... she's kind of like a shitty version of Alice.
No, seriously. Alice (who carries a slightly better level rate) has only a little less HP, the same DEF growth, much better MND, and a FIR nuke that's about as strong as Fujiyama Volcano except much cheaper with a much larger SP pool; and actual good random battle skills unlike Mokou. She even carries the offensive debuffs like Mokou does. The main issue with Mokou is her job is completely done better by so many other characters.
Sakuya, built offensively, can do okay with Killing Doll (only okay) in combination with her speed buffs to speed her up, assuming you're running Iku to keep her ATK buff up (Otherwise Killing Doll does very bad damage, but Iku is the best anyway). Built defensively, she should actually make a pretty good tank, with speed buffs to help her switching capability and support the party overall.
Yukari, built offensively, is terrible. No, really. Shikigami+ is a powerful nuke... IF both Ran and Chen are out when she casts it. If even one isn't, it's power drops SEVERELY. Her other attacks suffer from weak formulas and her MAG stat being less impressive then it might seem due to sluggish leveling. Due to her stellar support skills, it's far better to build her as a tank, which is a position she excels at. Even if you really wanted to nuke with her anyway, you have to fill three of your active slots (one with a party member made of glass) for it to be good, and if one of them (*Cough*chen) dies then the power drops even more, since there's a small boost if they're in your inactive party. Other nukers can do as much or more damage then an optimal Shikigami+ without having to fulfill any awkward conditions.
Noooow for Eirin. It's super, super weird that you're comparing her to Komachi o_O Eirin's HP is... average. The growth is slightly above average, but since her leveling rate is very slow, it's actually not. Her defensive stats will, in play, be about identical to Remilia with a similar build, except flip her DEF/MND and keep in mind she doesn't have the self-buff to keep them high, and about a quarter lower HP. She's still a nice tank, of course, but Hourai Elixir is really underwhelming. Even a different heal, or a buff, wipes out the bonus HP; and it's a pretty weak heal in comparison to any of the other healer options. 50% of someone's health is a number you'd be very disappointed to see from someone else's heal (Unless maybe it was on Komachi, which a proper healer should STILL heal more then Eirin), bar a MT one... which should still do better then that assuming that you should have some buffage on Reimu to make her heal a lot.
eirin is also slow and has high delay skills, when switching is one of a tank's critical jobs