Here's what we know about The Big A:
1. Was in Season 1
2. It's "Bittersweet" per Keegan Allen
3. It's twisted . . . (also per Keegan Allen)
1. The Twisted Version: Toby & Jenna have been a secret couple the ENTIRE time and are jointly A. We don't have a lot to back this up, but it is a pretty twisted guess.
2. The Bittersweet Version: Emily is A and the reason Paige suddenly left town & dropped Emily like a hot potato is because she figured out. Paige should've drowned her when she had the chance. We don't really have anything to back this up, other than it would be pretty sad if the sweetest member of the Liars gang was A.
3. Most Probable Version: Hanna is A. She and Mona (the first A) were best friends in Season 1. She's the most similar-looking to Ali. Ali humiliated her the most, making fun of her eating habits, her size, and the fact that her first kiss was with Aria's brother Mike. By Season 1, she was skinny, popular and re-invented with Mona's help. Remember Mona? She's dead now, but she was the original A. . .
Most of Hanna's A-prompted humiliations, like eating a bunch of cupcakes and bad-mouthing her soon-to-be step-mother at her father's wedding, were very public while those of the other liars were less visual.
Her mom was the first Rosewoodian to get put in jail, perhaps throwing the scent off Hanna? And Mrs. Marin would do anything to protect her daughter, including sleeping with Officer Wilden to keep her shop-lifting daughter our of juvie.
Let's talk about Hanna's men, shall we? Lucas was on Team A for awhile, and we all know he had a crush on Hanna. Caleb is a no-brainer with his cyber talents and "I would do anything for love" devotion to her. Then there was that little tryst with Wren at Radley while visiting Mona (re: Original A). And the time she kissed Officer Holbrook? Yep - you mustn't forget that Kodak moment.
Hanna vs the Liars:
Ali - Ali was the cruelest to her and the obvious target of her revenge. Hanna practically became Ali, aka the coolest girl in school, after Ali disappeared. She and Mona ruled the school. She needs Alison either gone or in jail to continue her reign.
Emily - Emily always loved Ali the best and in most seasons, was eager to do anything for the girl she loved. That might make Hanna dislike her.
Aria - (Still working on this one)
Spencer - She's a smart cookie. A spent a lot of time trying to get Spencer in jail, first for killing Ali, then for murdering Mona. It only makes sense that the Liar voted Most Likely to Solve for A, would be Spencer, therefore, she needed to be taken out first and foremost.
Hanna was also Ali's named "accomplice", and was the only person other than her mom and Jason who knew about that random night of MILF passion. A made sure it came up in Ali's trial.
Season 5 revealed how smart she is (getting a high score on the SATs and getting into Ivy League schools). She's had the smarts all along to run the A scheme.
Who do YOU think A is?