When making an awesome vinaigrette, your first instinct may be to reach for extra virgin olive oil - but a mix of neutral and strong oils can give you better flavour.
Image from grongar.
Use a neutral tasting oil (like canola or vegetable) to cut an oil with bolder flavour (walnut, sesame, etc.) Cutting with a neutral, and often cheaper, oil helps you get more out of those expensive, stronger oils.
You'll get a more consistent flavour since olive oils often vary from grassy to peppery. No matter what type of oil you use, make sure to use the ratio of three parts oil to one part vinegar.
How to Make a Vinaigrette [Bon Appetit]