The perfect fuel is the one that supplies approx 220 Kcal/hr, preferably with multiple forms of sugars and most importantly something you can stomach.. Seriously, the reason there are multiple forms of fuel is because one size will not fit all.
We can thank Ironman athletes for running fuel development. This all started with defizzed cola and salty solid foods then moved to putty bars. From putty bars, gels came about. Now the trend has started to include the alternative chewies. Wondering what a putty bar is? For grins, purchase a Power Bar energy bar. Cut it into 6-8 pieces and set up in the sun for 30-45 minutes, then pick one up to consume. Putty will come to mind.
One thing to look at with any sport fuel is the serving size. Most of the time, it is packaged in a 1-2 serving pack. I see lots of folks on course taking in one or two beans of other small bite sized fuel and wondering why it does not seem to be enough. The rule of thumb is to start with a serving about once every 45 minutes on the run. A serving is in the range of 100-150 Kcal.
One final thought, experiment with various brands, flavors and types. What seems appealing in the store may send you reeling while on the run. For many the flavor is chocolate - it seams to stick to the throat on the run for many.
Hope this helps