Hilda is cooler than Aoi, and she also has a sexier body.
However, she's also violent, self-centered and obessessed by her work. She would make a
horrible girlfriend.
On the other hand Aoi was written to be pretty much the ideal wife.
FOOLISH INDIVIDUALS!
DO YOU NOT SEE THE MAGNIFICENCE OF HILDA THAT IS HER TSUNDERE PERSONALITY?
WHILE SHE CAN BE ALL TSUN-TSUN, YOU MUST TRY TO UNLOCK HER DERE-DERE SIDE!
THE FACT THAT SHE WOULD HAVE AGREED TO BE YOUR GIRLFRIEND IS PROOF ENOUGH! HER DERE-DERE MOE SIDE MUST BE SHOWN AND TO THAT YOU MUST SHOW YOUR LOVE FOR HER!
Not really.
If Hilda is your girlfriend (rather than a fantasy based on Hilda) then she's most likely not your girlfriend because of any dere-dere moe side, but rather because she needs a roof over her head and a whipping boy to order around. Barring memory loss, she isn't tsundere because she's just pure tsun-tsun.