If you want to be miraculuos with your carb-up then you should have carb-powders that contain close to 0 sugar. i.e. dextrose
A good cereal is Corn Flakes, honey nut cheerios, or some other flake cereal. (not much difference)
I do not know of the best carb-up food, but I usually like to use some liquid glucose polymers like dextrose powder. Take a look at my CKD manual, I outline a sample carb-up there. www.elitefitness.com/articles