Love triangles despite being such a big deal in Macross tends to be less well implemented compared to Mechs and idols but Frontiers love triangle was perfect. Both Sheryl and Ranka are great and I love their relationship with Alto. Also felt like the love was balanced with their being a good back and forth between the two of them.
I think the best showcase of this is in the hospital scene where Sheryl and Ranka sings What Bout My Star duet for Alto. We see Sheryl sing the more provocative lyrics while Ranka sings the sweeter parts. We have Ranka's dance be cute while Sheryl's is seductive. All the while the romantic scenes between Alto and the two girls were put in really well timed flashbacks. I still vividly see the scene where Alto has both Ranka and Sheryl in each of his eyes.
Frontier is my fav Macross series and the love triangle being an all time great is a big reason why.