I've done some googling on this over the years and I've found that the Kirkland brand from Costco passes the tests given by whomever it is that studies this stuff and is actually extra virgin olive oil. I also think it tastes just fine personally. I keep a big container of that on hand for basic use like sauteeing, but I also keep a small thing of the really good stuff from local stores that specialize in olive oil for things like making salad dressing or drizzling on top of pasta or dunking bread into when you really wanna taste the good stuff. I buy the really cheap "extra light" olive oil, often just the generic brand or whatever is on the deepest sale, for making homemade mayo and I think it tastes really good (wouldn't want strong olive oil flavor coming through for that).
Their Kirkland brand is probably the best generic brand in just about every category. I had a friend who supervised a company that manufactured trash bags for a bunch of name brand and generic companies. Kirkland was as good as the name brands and by far better than any of the other generics.