Go by the nutritional labelling (i.e. total carbs per 100g) - "No added sugar" can be nasty weasel words, as some foods/drinks will have a natural (and sometimes high!) sugar content, and sugar is sugar in whatever form.
As for sweeteners, I only use stevia and erythritol (alone and in combination) as these don't raise glucose levels, are virtually zero calorie, and won't (normally) cause any "gastric upsets". Watch for sugar alcohols with names ending in "itol" as these will generally do so, exceptions being erythritol and xylitol. Also check ingredients - e.g. stevia is extremely sweet and in powdered form may have other bulking agents added in the form of starches, etc, to enable it to be used in measurable quantities, which can affect glucose levels. Stevai/erythritol is a good safe combination.
And finally many sweeteners will have a high carbohydrate content but these carbs don't get processed by our bodies, so don't affect our glucose levels - but as I've mentioned, may have some unpleasent side effects instead. So it can pay to so a little homework!
Robbity