Blonde never saw him before he changed so that can’t be used against him, he saved her life not once but twice now and that’s why she wants to marry him.
Still prefer the black hair girl cause in exchange for saving her, she found out he was getting bullied and helped him to change schools and made sure he was comfortable not only at school but with himself while the princess got saved once and just proposes before atleast saying thank you. Plus the black hair girl seems not annoying and intelligent which makes her more refreshing to read than the princess who asked her dad to go back into the forest that tried to kill her for a dude she didnt know and had to be saved again.
The blonde girl doesn’t even know he’s from another world so his life in his world is irrelevant to the topic all together, I’m not saying black hair girl isn’t the better choice I’m saying y’all judging blonde for not knowing his past look when that’s out of her control.
Then I'm judging blonde for this - she knows that the forest [] is a lair for the strongest demons, even Demon lord can be found here, but still "lets go to that forest so he can hug me again". Damn, girl, you're a princess, have some bare minimum sense of danger and be aware that your escort needs to be extra vigilant in such a dangerous place because you're weak and cannot protect yourself.
And of course she is generic damsel in distress of the worst kind. She don't even know his name and demanding to marry her is a top of any stupid fairy tale ヽ(`Д´)ﾉ
Please pick the black haired girl instead of the princess because she accepted him even if he didn't transform