The standard "sweetener" liquids sold by most DIY suppliers is sucralose, which is a synthetic sugar that is SUPER sweet--600 times sweeter than table sugar (sucrose). It is the main sweetening ingredient in Splenda.
Some folks (like me) who do DIY are a little wary of synthetic sweeteners, and have tried liquid Stevia. I've used it in several of my DIY mixtures, and I think it works just fine. Not as intensely sweet as sucralose, but then again, it's natural, not some lab-created franken-sugar. Some brands of Stevia liquid can have a liquorice or bitter aftertaste, so don't
buy the cheap brands.
The "onset" of the sweetness of Stevia isn't as sudden as sucralose (or even real" sugar), but the sweetness lasts longer in your mouth, so if you use Stevia for DIY liquids, give it some time when you're test-
vaping your mixtures. It sort of creeps up on you, instead of smacking you in the gob with sweetness. It's easy to over-sweeten with Stevia--and when you do, it tastes like crap all of a sudden...