Ah, finally a poll free of bias. Obviously the best is our one true empress Edelgard.
Honorable mentions include Petra (definitely the MVP in battles, looking like MUI Goku out there)
Mercedes (the ultimate healer, shame about the timeskip design though, why cut all that fluffy hair :( )
Marianne (also a great healer and could do some damage on the side, I also constantly wanted to give her a hug, poor girl)
Lysithea (the killer mage)
Hubert (pretty smart dude overall, also pretty killer on the battlefield)
Hanneman (love how generally chill and supportive he is of the students)
Shamir (great archer with a no nonsense attitude) Bernadetta (also a great archer and she has some pretty funny supports)
and Dorothea (great overall support unit and I liked a lot of her supports).