One of the most frequently asked questions I receive is, "What is the best oil to use for cast iron?" This can be a very simple, but also a very complex answer. The oil you use has to have a very high smoke point.
Any cooking oil that is lower than 400 degrees is not recommended as a seasoning oil. Oil with a high smoke point is the absolute best for your pan. When the smoke point is not high, the oil becomes a sticky mess. After a while the oil can become rancid and leave a pungent smell. In some cases, I've seen mold grow on the sticky patch of oil.
The smoke point is the burning point of the oil. Once the smoke point has went passed the burning point, the oil breaks down and becomes a film, and no longer an oil. The film becomes the seasoning. The seasoning needs layers to protect the food from sticking to the pan.
How do you find the smoke point of an oil? Easy. Glad we have Google for that. There are several lists that have the smoke point of several oils. After I clean a cast iron, I wipe down my iron with veggie oil. Veggie oil has a smoke point of 400 degrees. After my first round of seasoning, I add bacon grease or rendered hog fat.
There isn't a magic oil in the cast iron community that will promise glorious results. Testing your seasoning by cooking in your cast iron, will tell you a lot about the oil that you used. For me, it's one round of veggie oil and two rounds of bacon grease, or rendered hog fat. After seasoning is complete, I add a few more rounds by cooking bacon in my skillet. Cooking bacon will benefit your cast iron seasoning by adding more layers of seasoning and protection.