Maybe it's just because my interest in EqG isn't as strong as my interest for "regular" MLP, but although they share a lot of personality traits (which is hardly surprising, obviously. :P ), they are different characters and I simply haven't found Sci-Twi to be as endearing and lovable as our adorkable pony princess. :P
By the time I write this, we have 13 for Pony Twi, 3 for Sci-Twi, 5 for both. 13 Is supposed to be an unlucky number, but apparently not this time. I'm considering giving me more space of time to update this because I feel not everyday I'll have something relevant to say here.
I dislike Sci-Twi, because Sunset Shimmer was supposed to be EqG’s Twilight and having this second Twilight just feels awkward. She doesn’t have enogh history with the Mane Six to me, so forcing her in has always felt unnecessary and lame. It would’ve been cool to see her as a one-time character, but I don’t like her as a main addition to the series. Especially since now she’s sort of considered the main girl, despite only recently meeting her friends. Their friendship feels forced and fake.