The liquid Sweet 'n Low has the advantage that there are no other ingredients to bulk it up - and those incredients typically carry on the order of one carb per serving.

I don't use it because I dispise the taste (and aftertaste) of saccharin. I haven't noticed any aftertaste with Splenda (though others have) but I also don't use it except very sparingly - in fact I've only used it on four occasions so far.

You won't find Sugar Twin in the states because it is still banned here even though all of the health scares about it have pretty well proven to be bogus.

Can't help with the on-line stores I'm afraid - the only one I have purchased from is Atkins when I bought my vitamins.