My (good) red units are 5 star Lyn, 4 star Chrom, 4 star sophia, and a 4 star Olivia who isn't so strong. I have 3 spear users, 4 star Oboro (with heavy spear), 4 star Peri, and 3 star Subaki. I never take Peri or Subaki to Arena cause Subaki is thick but doesn't do enough damage, and I don't know if it's my Peri in particular but she has no particularly good stat which kind of makes her "meh" in my opinion. Oboro has nice attack and she's as thick as anything so I use her as a sack in arena a lot. Not to mention her rally defense AND seal defense AND threaten resistance which is super helpful in getting of some chip if Lyn doesn't insta-kill any of the Psychopathic 5 stars in Arena. I also have Gordon and Serra to heal for neutrals. But then I have 2 ax users who are both too weak to live through anything since the vast majority of 5 stars are red. So that's my ally situation. My main team is Oboro Lyn Barst and Serra, all pretty much have max skills except Lyn who doesn't have spur speed 3 or Galeforce yet.