Teammates for Micaiah

I would say some1 who can take out high res foes, like fliers.
a good archer would do for a start :)

The Offensive set is a lot better for her because her her physical defenses are really low, and her low speed means that even strong mages (or reinhardt) can kill her.

In Brash Assault range she will kill every armor an horse without worry, including Berkut Lance Effie, Sheena, and Titania (but, importantly, not WE!Lissa) though it might be tricky to get her down to 18 HP.

Where she needs help is against non-reds with good res, mostly Dragons and DC axes. A strong sword, maybe even a falchion like Lucina, would be a good teammate in that case, as well as Nowi with Breath of Fog.

You will also want a green that can either tank and kill strong blue mages. Armors like Henry, Grima, and a DC Amelia/Sheena can do it but some infantry options are Julia/Deirdre and DC Brave Ike.

What are the best units you have in these categories?

Have you worked on the question yourself? There's even a section on every character's page that suggests possible teammates. I don't always think the analysis covers a good variety of options, but it's always a start. You play the game. You understand things. You probably understand her better than me because you actually have her. Give yourself some credit and try out some of your own ideas.