Best horse emblem team as of now ?

Mb Legendary Eirika? Red, melee, provides legendary atk buff, and I believe she can kill stuff.

I agree with oudam. Either Legendary Erika or Hrid if you have them. If you don't, Xander should be perfectly serviceable.

Hrid. Lancebreaker on reinhardt.
In aether raid for the fifth slot, gunthraa or any dancer is the way to go

Hríd is ideal. Sigurd I would say is second best, followed by other tanky cavalry including barrier blade Seth.

If this is for Aether Defense just throw on dancers or a bladetome horse. If this is for personal use I'd probably get a melee tank like Silas.