I use only extra-virgin olive oil from Italy (italian olives, italian producers), not just because I'm nationalistic (which I'm not), but because I've always used it for every task in the kitchen with decent results. I make an exception only when I need to cook something with butter (risotto, eggs, milanese cutlet...), and I do not deep fry, so I never consider using cheaper oils.
In Italy we have a wide variety of different EVOOs, from those produced by industry giants, like Bertolli or Carapelli, to those made by small, local producers, sometimes with an organic approach. And the taste can be greatly different: you can have very "heavy" oils, like some from Puglia, or more delicate ones. If I need to use EVOO for cooking, since I try to use only a little amount, the taste of oil doesn't matter so much to me, but if I must dress a salad I tend to prefer the more delicate.
And I admit I never studied seriously the chemical properties of olive oil: we've been eating it from the time of ancient Greece and Rome, so I suppose it's a good food. May be not, but I'm so naive sometimes...