I think 10, 12 & 13 are all pretty open at the moment. Beale would have to be ahead for 10 at the moment, if only because he's the incumbent, but I think that on balance over the last three years he's played his best football at 15. For mine, Cooper hasn't done enough to erase my memories of 2011, his form this year has been unimpressive, and unfortunately neither Lilo nor JOC (James O'Connor) are playing 10, so it makes it hard to assess these two principal candidates. To'omua may yet be the one, but I think it's too early to say that.
For mine Tapuai is the best option at 12, but perhaps JOC (James O'Connor) if he isn't going to be 15. No-one is really demanding to be selected at 13 right now, which probably leaves AAC (Adam Ashley-Cooper) in the frame, but he's hardly set the world on fire at the Tahs this year. To me AAC (Adam Ashley-Cooper) should always be on the bench, because he is reliable and can cover so many positions, but you would like to think you could find a bit more class for all your run-on positions.
To add to the earlier debate about the qualities for a great 10, sure all the run, kick, pass, defend qualities are important, but the best 10's I ever played with had vision. After all, it is principally going to be at 10 where the decisions are going to be made about what we are going to do with this use of the ball, and the really good ones are able to feed everything they see before them into the mental computer, and in an instant come out with an option that 9 times out of 10 is the right one. Obviously, as you people have pointed out, he then has to be able to execute that option.