I would recommend C++ for games in general or python for history-oriented games such as visual novels, point and clicks, simple adventure types.
But let me ask you a question, have you finished a game with AS3? I mean, the language you are using is really not that important in the end, since you can change it how many times you need. But being able to finish something is really one you need, above all languages.
So, my final word is stick with AS3 until you have finished a single game. After that, you can probably choose any language and you'll be fine.
I have finished one small game for my school as final project, a knight duel game, a reaction based game with mix of rock-paper-scissors mechanism for two players on same screen and computer, which was about year ago, and from that I have moved on to more ambitious projects that I have not yet finished, nowhere near. One project I actually had to scrap because it was too ambitious and became such monstrosity that I didn´t even know where it was headed, though I have salvaged a lot from that thing which have helped me on my current less ambitious projects.
And yeah, I have few projects going on with AS3 that I will finish... I didn´t say it clearly, don´t know why, but I was thinking of learning some new language after those.
Don't know why are you moving from AS3, since it has Flex+Starling+Feathers which give you the simple mechanism for 2D games making (out studio is making the game by means of those tools right now). Anyway, if you want something similar, you can try JavaScript and make games in HTML5. JS and AS3 are almost identical. The only major difference is the code structure - JS doesn't default anything to class. If you want something more powerful for PC, I would recommend C++.
I am thinking of trying to switch my focus from AS3 to other languages since everyone who have been doing this so much longer than me, including teachers say that flash will be dead... And I am really these years taking my first steps, so I am at good position to learn new language. (Also, maybe I just need to grow thicker skin against naysayers? )
Anyways, Java sounds like something that might suit my needs better than C++... though that Adobe CrossBridge sounds really neat... >_<