I don't think Alison is Uber A, my money is definitely on Aria. Obviously, it would suck because she's one of the Liars, but there are just way too many clues pointing in her direction.
She came back to Rosewood after being in Iceland for a year and the Liars start getting harrassed by A. It was never really disclosed why she was in Iceland. I wouldn't be surprised if she had some sort of personality disorder; the whole mirror theory and the changed appearance when she came back. Also how she has changed through the seasons personality/mood wise. Not surprising when you're bullying and killing people all over the place.
And when you compare what A has put her through, to what each Liar individually has been through, it's not as heavy. Not saying she hasn't had it bad, but still not as bad as the others. Mostly bad things happen to the people she's connected to.
Then there are the obvious things: Her name starts with A lol.. Aria is the one who does the 'Shhh' in the intro. She's the main focus in the first episode. The first text she gets in the pilot (either that's a mistake the writers made, or it's genius :-)). The various phones she apparently owns etc.
But I don't think she was the one to hit Ali with the brick. I think that was Bethany, who was probably jealous of Alison. It would explain why Jessica would be protecting someone. I think Aria killed Bethany by mistake, thinking it was Alison.
I also think there are different people behind the A-messages. Obviously the A-team, but I mean it's also noticeable for the viewer. Example, Aria only gets individual texts from the person closing with "--A". The rest of the Liars get texts closing with both "-A" (=Aria) and "--A" (Mona). Collective texts are also from both. The ones closing with just the "A" are from Alison I believe. And then there are also the written messages with the various handwriting etc. It's so amazingly well thought out! Okay, I'm gonna stop now lol