A. I think Greece produces the best olive oils, but it is usually bought by other European Common Market countries that blend it with oils from countries like Turkey, Italy, the North African countries, so it is rare to get a pure Greek olive oil in the USA. Certainly there are wonderful olive oils from Sicily, from Spain, from southern France.
There are a few terms and practices that can help you choose the right olive oil. A cold olive gives less oil, but of a better quality, than an olive that has been warmed by the pressing-plant operators. So the words "cold pressed" are an important indicator of quality. The term "extra virgin" is also always a good term to see on a label. Color does not mean very much. Olive oil can be artificially colored if a certain shade is desired. Currently people think the darker green an olive oil is, the better, but that is not so. The first real indicator of the quality is the smell.
Next, you should put a few drops of the oil in the palm of your hand and rub it with your finger in a circular motion. This will give you the feel of the relative viscosity of the oil. A lighter viscosity is better. Also, if the oil has been colored, this is when you can see the color come out towards the edges of the spot you are rubbing. Then taste the bit that is on your finger. A lower-quality oil will have a very slight peppery quality on the tongue. The absence of this pepperiness is a sign of the best oil.
Beyond that, choose what you like, but remember that it is a complete waste of money to fry with a great olive oil, because heating destroys all the subtler flavors. Also you can blend a little, maybe in a five-to-one ratio, of good oil with great oil, and get a delicious product at a somewhat lower cost, because the very best oils are very expensive.