I mainly use Eirika, Priscilla and L!Azura + Bonus Unit for TT. Duo Micaiah is now mainly here for picking off strong blue cavalry and armours which can damage Eirika a lot even after Repel.
I always had to deal with Surtr with a general red unit, usually Lilina or Eirika + Dancer. Didn't get a good anti-armour unit until after he was removed from the random unit pool.