dextrose is sweeter so if malto wasn't sweet enough i'd go with dextrose.
you might think of trying something like this?
True Protein | High Quality Nutrition and Protein Supplements
looks like it has some of each. If you want it sweeter,just go to custom, and up the dextrose and lower the malto. At least now you have a good jumping off point on where to go.
Hope this helps!