I'm positive it's going to be Black Cat. I don't think there's any question that the rights to Jessica Drew most-likely lie with Marvel, not Sony. The only connection the two characters have is from Ultimate Spider-Man where a female clone of Peter called herself Jessica Drew, but that's hardly a Quicksilver/Scarlet Witch situation. If Sony tries for a Jessica Drew movie, they'd have a massive uphill battle to prove that she's part of the Spidey rights. Fox would actually have more of a claim to Drew's rights, since she's spent more time in X-Men comics than in Spider-Man.
Julia Carpenter had a slightly stronger connection to Spidey, but that mostly came about later in her career when she became the new Madame Web. The only Spider-Woman Sony could really make an airtight case for is Mattie Franklin, but I doubt they'd want to make a movie about a teenage girl with spider-powers, because that's not enough to differentiate her from Peter.
A Mayday Spider-Girl movie is also unlikely since Sony wants to build its own little universe, and doing a movie set in the future wouldn't really work with that. That also means we won't be seeing any Spider-Gwen movies set in an alternate universe.
The Anya Corazon Spider-Girl is more likely than Mayday, but once again there's the problem with a movie based on Mattie Franklin—not really enough there to differentiate her from Spider-Man. The mystic background of her powers would help, but I doubt Sony wants to go down that route.
This makes Black Cat the most likely candidate. Sony knows they've already got the rights. They've already had Felicity Jones play a pre-BC Felicia in ASM2 so the casting is done, and this allows it to tie into ASM2. A Black Cat movie could also be potentially cheaper to produce than a Spider-Woman/Spider-Girl picture, plus she's got enough to differentiate herself from Spidey. Black Cat for the win, IMO.