There is also natural stevia powder (green) This is the whole stevia leaf ground up and has a strong aftertaste which cannot be removed...it is the most natural form of stevia with the most nutrient value however most people do not like the strong taste...it can also be acquired un-ground in a "tea" cut which is good for adding to herbal tea mixtures...
...and then there is the pure Stevia Concentrate itself (white) ...the quality can vary hugely and this is where it becomes a little tricky...
Unfortunately stevioside is the most widely used in N. America because it is less expensive and more readily available. In Japan where stevia is consumed widely they use almost exclusively the Rebaudioside A leaving the more bitter stevioside to be used in pet food where the consumer (Fluffy, Fido, Spot etc) is not as concerned with aftertaste.
...making it a clean, pure and incredibly sweet taste, (approx 300x the sweetness of sugar) .