Basically there are 3 main sweeteners used in vaping.
Sucralose (most branded sweeteners sold by flavor manufacturers are just Sucralose in PG), has an artificial sweetener aftertaste.
Ethyl Maltol (aka EM aka cotton candy flavor), many flavors also contain small amounts of EM, too much EM mutes the flavor.
Stevia, too much leaves a bitter aftertaste, comes in grades based on percentage of REB-A (higher grade means less bitter aftertaste).
While EM acts as a sweetener by enhancing the sweetness of other flavors, the other two are actual sweeteners, Sucralose is 400 times sweeter then sucrose and Stevia is 250 (more or less) times sweeter then sucrose.
There are many other sweeteners used by the food industry that are not viable for vaping, either because they are not sweet enough (Sorbitol, Maltitol, Erythritol...), because they don't react well with heat (Aspartame...) or because they caramelize (Fructose, Sucrose, Glucose...).