Having said that, there are still distinctive categories or types of extra-virgin olive oils for which each is best suited in terms of preparing certain types of dishes.
Just as you would likely cook seafood and fish with white wine vs. red wine, each type of olive oil would offer distinctly different flavor.
Olive oil and wine are comparable in that they are both the juice from fruits. Just as there is no wine which is "the best", so there is no one extra virgin olive oil that is better than all others.
The differing properties of individual oil depend on the ripeness of the olives when harvested, how they were kept and how the oil was extracted.
Olive oil can be judged by its taste alone. For example, oil is termed fruity when its flavor and aroma are similar to that of a mature olive. Some people have heard that good olive oil is always green.
However, the color of the olive oil is never a tasting factor. Professional tasters even use blue glass snifters to disguise the color of the oil so that their judgment will not be affected by the color.
Good flavor is the result of picking healthy fresh fruit at the optimum stage of maturity. Immediately after pressing, all oils seem fruity, but in most cases, this characteristic disappears after a few months. When an olive oil is described as fruity, it means that this characteristic aroma remains through time for at least two years if stored properly.
Fruity-spicy olive oil preserves the longest as well.
In order to get the best out of your tasting just cut a loaf of white bread into small pieces. Pour the olive oil in a small plate and dip. In order to avoid mixing flavors, have some water in between or even better, have small pieces of green apples between each tasting.
If you still can't distinguish one type from another, don't fret. It takes time to learn how to distinguish one type to another. People actually attend classes to learn tasting tips and techniques just like wine.
There are many olive oil tastings as there are wine tasting. It's a great way to test them out and see which types you prefer. Check out the directory for tastings and tasting bars.