Diaspro because despite that she's a fairy herself, she still acted more of a villian which made me think she should have become a witch like the Trix instead as Diaspro is cunning and devious as shown back in Season 3, Season 5, Season 6 and Season 8.Diaspro will never give up or accept that Sky loved Bloom and no doubt she'll keep coming up with another cunning devious plan to break them apart .
I mean Diaspro could have taken down Bloom herself instead of relaying on tricks but her fairy form is weak and she doesn't like to work hard, while Bloom worked hard to earn more powerful fairy forms like Enchantix, Believix, Sirenix, Bloomix, Butterflix, Cosmix and Crystal Sirenix. Which is why Diaspro won't stand a chance against Bloom