my 2¢ ...

No matter what is the actual chemical they're made with --- aspartame, saccharin, sucralose, acesulfame K or cyclamate --- ALL of the powdered sweeteners have maltodextrin as the filler.

Maltodextrin is spun from modified starch .. usually corn or barley. It's "supposed" to be tasteless, but IMHO, it gives a bitter, almost sour aftertaste. You don't really notice it when it's a small amount, a couple teaspoons or a packet ... but when there's a larger amount ... blecchhh! Mixing sweeteners, as Nat suggested ... does soften the edge a bit, and enhances the sweetness.

Technically, aspartame, sucralose, cyclamate, ace-K and saccharine are known as intense sweeteners. So besides the bitter aftertaste from the maltodextrin, I think the sweet taste becomes more intense and concentrated the more there is of it in a recipe. So, 1 tsp of splenda or sugartwin may be the same sweetness as 1 tsp of sugar ... but 1 cup is WAY sweeter.

Doreen