Which unit to promote first

I have a few 4 star units that i want to promote to 5 star, but i'm not sure which one. I have all the builds planned out. Here are the heroes i want to make 5 stars:

1. Eirika with rally resistance and fortify def 1 sacred seal
2. Masked marth with reciprocal aid, renewal and breath of life
3. Effie with brave lance+ wary fighter and death blow

For eirika, i feel like she would be really good at supporting my two blade tome users Nino, Tharja and male Robin. For masked marth, the only other falchion users i have are regular marth and alm, so she would be great for me. For effie, i already have an effie maxed out at 5 stars with +HP -def. I'm not sure which hero i should promote first and which should i leave behind

P.S: I will be getting the 5 star black knight, so he is out of the question for now