That will depend on your own likes and dislikes. Most of the fruit flavors I've found are naturally sweet, especially if you use 10% + flavoring. There are those flavors that are almost there and need a little extra sweetening boost and then there are a few that are very dry and desperately need sweetener. TPA Black Cherry is a prime example of a fruit that IMO must be sweetened to enjoy. The best advice I can give you is to mix, taste, and then go from there if you feel it needs sweetened in order to arrive at what you want it to taste like. Sucralose is stout sweetener and a little goes a long way so work your way up. EM is softer and will require a bit more. Once you are familiar with your flavors, you might find that you can hit the mark by adding another flavor rather than using a sweetener. Marshmallow is a great flavor for adding sweetness and a smooth creamier flavor. Just play around until you find the right one.