Sci-Twi is kinda whiny, and sometimes self centered because of her insecurity. Regular Twi is sweeter, cuter, friendlier, and has learned more life lessons. She'd be an awesome girlfriend for Sunset. And eventually Sunset would go back to Equestria, because she doesn't really belong in the human world, like she won't want to go to college. She should definitely pick Princess Twi, and be her sun queen