Continuation Bets

[Macedon]

I would like to hear people's opinion on Continuation Bets in NL; specifically, how much is reasonable and what can your opponents read from betting too small or too big.

Here is a typical case where this problem might arise:

You have AKs/AQs in late position or the button.
One or two players merely match the BB.
You raise 3 times the BB (or some amount close to that).
The Big Blind and MP1 calls.
[The pot: $9]
Flop: 2-5-9 rainbow

[For the sake of argument, assume that your opponents are average players and their stack sizes are equal to yours. I am looking to reproduce a very generic example here.]

If both opponents check, how much would you lead out and bet?
Pot size: $9
2/3 pot: $6
1/3 pot: $3
Or would you check behind them?

If you bet pot size, aren't you saying, in effect, that your hand is vulnerble, for if you did have a better hand wouldn't you (in their opinion) either bet small to get them to call OR check and let them see a free card so you can punish them on the turn?

If you bet 2/3 of the pot wouldn't your opponents suspect that you don't have THAT decent of a hand and you are trying to buy the pot? Or perhaps the bet is small enough to give them decent enough odds (actual or implied) to see the turn, especially if they were lucky enough to hit one of their low cards.

And if you bet $3, aren't you sending out the signal that you hold a poor hand and are merely hoping that your opponents have a worse hand? Wouldn't that be a reasonable conclusion for your opponents to draw from such a meagre bet? Or would they suspect you have a monster and are trying to suck them in, or induce a re-raise?

As you can see, there are so many variables involved with a continuation bet. Are there any good tips/thoughts anyone has for determining what to throw down? I'd appreciate comments.