Ethyl Maltol has been discussed elsewhere on ECF and at length by member(s) we2arecool who did exhaustive double-blind testing on many aspects of DIY. Other characteristics aside, EM will sweeten, but not very much and then only for liquids which are not in and of themselves as sweet as EM. It is better used as an enhancer as danny45 describes above than considered a sweetener at all.
Sucralose is likely the most often used sweetener in DIY. It's not perfect but will definitely sweeten in cases where EM is ineffective. Some DIYers can taste an artificiality or bitterness. Almost every brand or vendor offering labeled 'Sweetener' is Sucralose.
Marshmallow is, for myself, an effective sweetener in many
e-liquids and I have a 60ml bottle for that use almost exclusively. Since there were opinions expressed to the contrary, I suppose we could say it is arguably and effective sweetener.
FA Meringue can sweeten certain
e-liquids and in some cases enhance them. So it is when combined with FA SoHo. It will also add a 'baked' quality to juices, such as providing a 'browned edges' effect to a cookie vape.
Stevia seems too be the latest DIY darling and perhaps it earns the praise. Available inn pure powder or unadulterated liquid form. it is sugar-sweet without sugar and adds no bitterness YMMV, as always but it opting for the liquid, it's wise to be certain there is nothing other than bases one would use in mixing: distilled water, PG, VG or ethyl alcohol. My preference is powder for greater control.
ETA: As #
sketchness pointed out, there's no reason to add any sweetener unnecessarily Try any recipe without sweeteners before adding any. Flavorings are sweet and may well be sweet enough.
Besides being economical, mixing one's own e-liquids adds a myriad facets to transform our lifestyle into something that is ever more deeply satisfying and rewarding.
