Who stays on armor emblem vs who converts better to mixed team?

Hector is still the king of enemy phase units, no one is better at a base level then him when it comes to counter kills, and if you can get the new Bold Fighter on him he'll be a great player phase unit as well. His legendary weapon gives him so much more build freedom then W!Chrom can hope to compete with.

So I personally think Hector is better both on an armor team as well as in a mixed team.

But that being said W!Chrom is basically a green Effie, potentially even better at her own role with higher atk then hers as well as an inbuilt Wary Fighter. So if you want an Effie like unit on a team but already have all the blue units you need on that team then W!Chrom is an amazing replacement. Largely cause he's better then Effie, he just has more competition in the green category then she does in the blue :P

Lack of mobility means it's harder to use your mixed-team armor as a player phase unit.

With his monstrous attack stat and OK defense, your W!Chrom would do better on an armor team, where he can get armor buffs and be amazing during both phases.

A +Def Hector is definitely more of an enemy phase unit. His high Def makes him less dependent on emblem buffs to survive on the enemy phase.