what you think is better?
I would avoid aspartame, however I don't worry too much about sucralose. A little bit of artificial flavouring isn't something I avoid either, I don't really think there's much health risk. However there are some purists who try and remove all artificial ingredients, hence the Natural product.
Any particular reason you're sticking to ON? I would recommend trying the flavours from AllTheWhey for a change,
Products By All The Whey . Cupcake Batter is interesting, and Cinnamon Bun is my all-time favourite; this stuff is amazing. The Lean & Fit is an isolate and quite well priced, or you can go for the blend which I usually opt for at only $30! Their chocolate and vanilla are pretty good as well, although ON 100% has some pretty good novel flavours.