I have both New World and SmarTone, and I'd recommend SmarTone by far... I bought the card at a booth on the side of the road that was advertising "International IDD Calling" which I know not what it really means, but I've heard that it is the cheapest method of calling. So I tried it out, and so far have made about 5 calls to the US (about 20 minutes each) and have yet to recharge. So that means for $100 and 100 minutes, at worst it is 1$ a minute for international calling (from a cell!!). Pretty good, I think. It advertises it at 50 cents a minute, but I can't confirm if it is THAT low.
As for text messaging, I'd say it's not worth it. It costs about 2-3 dollars to send one sms internationally, and for that money, you can talk to them for 2-4 minutes.
As for CSL, my friend just got his bill yesterday, and while he sends no more text messages than I do, and perhaps makes a few more calls than I do, his bill was about 3 times of mine. So unless I'm missing something, I wouldn't recommend CSL.
[edit] another comparison: CSL 1000$ prepaid card: $.3HKD/minut----New World X$ prepaid card: $.22 HKD/minute