My opinions for all matchups:
Justice - Khagan: Blame Dschinghis Khan for this choice.
Elena - Rumpelstiltskin: Despite being as resilient as tissue paper, Elena looks like the kind of girl who’s not fooled by trickery and will NEVER give up a fight!
Leonidas - Joon: Chosen by design.
Red Hood - Queen of Hearts: Red Hood’s tiny waist disturbs me. And I do like the idea of a ‘taunting’ Tank!
Alice - Domitia: Domitia ■■■■■■ me off with her Holy Resistance. And I LOVE looking at Alice’s bouncing dress. 
Burger Kong - Lianna: An odd choice, but thanks @Hrairoo for this beautiful meme:
King Arthur - Kadilen: Well… I think the Excalibur Special looks cool. 
Azlar - Marjana: Barbarian Lion Man Dad? HECK YEAH! 
Magni - Sartana: Mostly because I dislike Sartana’s artwork.
Captain Kestrel - Lady Locke: Didn’t care about either, but I think I enjoy looking at Kestrel more.
Morgan Le Fay - Richard: The Hammer conquers all! Both of them actually. 
Mad Hatter - Obakan: One of the ugliest Heroes of the game, facing my first 5* Hero with a cool buff steal effect? Easy. 
Captain Sargasso - Vivica: Can’t hate Holy dragon-taming connoisseur scholar Chinese girls. 
Horghall - Elkanen: Kadilen’s brother looks so stiff in his artwork. So I voted tree. 
Quintus - Thorne: Stop picking on elders with artificial limbs. 
Isarnia - Boss Wolf: The Beast is so much better dressed, it’s not even funny. 
Besides, how didn’t Isarnia freeze to death?