I wouldn't use the initial cavaliers (stahl is ok if you find a good reason), Vaike, Sumia (just good enough for an adequate cynthea), Kellum or Ricken. They can still be good pair up units and while Ricken is good for counter Robin or Mirial should already outclass him. Kellum is easily gained up on and is nuked by a counter hit because of high damage, he is dual striked and has awful resistance. His defence virtue is lunad out too. Vaike is a good pair up with a +4 or higher in str (I would use Nowii because of the stat mods for Nah.) Marible isnt great but is redeamable. I always found her to difficult to grind and lissa or libra just was always better.