Phoenix – About.com User
Another reason it's difficult to answer this question (in my opinion) is due to individual taste. I mean, if you don't like blueberries or broccoli, there's not much point in buying them and forcing yourself to consume them. Fortunately you don't have to. Hate broccoli? Eat kale. Hate asparagus? Eat green beans. Hate apples? Eat strawberries.
There are also things like availability and storage factors to consider. Raspberries are good for you, but they're so delicate and they go bad quickly. No superfood fruit or vegetable is going to do you any amount of good if you have to dump it down the garbage disposal, toss it in the compost, or feed it to the squirrels in your back yard.
So I guess my final (and maybe it's wishy-washy) answer to your question is that there is no one best fruit or vegetable, except for the one you love best. Unless it's French fries or apple pie. In fact, don't torture any of your vegetables and fruits by deep frying them or turning them into high-calorie desserts. Eat a rainbow of fruits and vegetables every day and you'll be sure to get the variety of nutrients you need.