I tried to narrow this down to just one, but couldn't manage it... so here are my choices for favorite non Fairy Tail characters.
Millianna - Mermaid Heel
I have to choose Millianna because she tries really hard, is great comic relief, is awesome enough to have fought with Jellal's group for a while and she's really cute with the car ears.
Minerva - Sabertooth/ Neo Minerva - Demon
Minerva seems cold & vicious, obsessed with becoming the strongest & even becomes a demon in order to beat Erza & be the strongest. Few insights to her true self are shown before the ending of the Tartaros arc. I personally think she is yandere af, but maybe a touch of tsundere by her crying at being welcomed back to Sabertooth. The future will hopefully tell.
Flare - Raven Tail / Sun Village Flare is a character that should get more screen time. I actually hoped she would join Fairy Tail but didn't happen. She does seem to be out in left field when you look at her due to her large eyes & blankish expression, but she is actually shown to be more naive because of her upbringing & Raven Tail being her first experience with a guild. Having a perfect hour glass figure and long red hair don't hurt eithet
Frosch - Sabertooth
Frosch is pure comic relief. I enjoy episodes he's in more because he's just so.... Frosch.