All natural or current version, I'd be in favor of the larger size if the cost per serving went down, as w/ most products. I think there are enough fans of Rag to not have to worry about whether the larger size would sell.
As far as the natural version, I'd probably try it if the taste were comparable. Are the natural sweeteners more expensive to purchase than the current ones? How much of a price difference would we be looking at between natural and current versions. These are a couple of the things I'd want to know before saying for sure what I'd prefer.