I've found that they do have definite preferences. Feeding container type and placement, brand/type of sugar used, water used for mixing it up...even tools used to make the food can make a difference. I don't know why, but they do.
I do tend to make my mixture very syrupy...definitely not clear. I don't measure anymore, but the most loved mixture feels thick during stirring, and has a somewhat beige cast to it...most notable when using a white ceramic bowl or cup to mix it in. I now keep dedicated stuff just for them; the aforementioned bowl, a coffee cup for early or late season small batches, a wooden spoon, and a toothbrush for cleaning. These never get washed with soap...just rinsed in hot water and dried with paper towel. Two things they seem to be most sensitive to are soap residues and sun-baked plastic feeders. No matter what mix you use they'll attempt to look elsewhere for food.
