What is the best substitute for safflower oil?

Canola oil is a vegetable oil, pressed from the seeds of the "canola plant" - an engineered variant of the rape plant, which was given a trademarked and much more marketable name in the 1970s. Like corn, peanut, safflower, sunflower, soybean, cottonseed, and some other vegetable oils, canola has a neutral taste, so there's really nothing about it to strongly dislike.

The various canola trade associations call it the "healthiest" oil, because it is lower in saturated fat than any other common oil, yet high in unsaturated fats and free of cholesterol and trans fat.

If you don't have it on hand, use any other neutral vegetable oil. If you can tolerate a bit of flavor in the finished product, you could use an oil with a stronger taste (for example, olive oil). Be sure the flavor matches what you're making, though ... olive oil is probably fine for mayonnaise, but walnut oil may be a better choice in a cake (that said, I'm aware of cake recipes that specifically call for olive oil; you're the cook, do whatever tastes good to you).