Having grown up in the southern US, the traditional seasoning of cast iron in those parts was to simply cook bacon in it a few times. Nothing near as fancy and involved as what you see recommended these days. That has been my usual lazy approach.
On a recommendation from a cast-iron retailer, I have started using the new fancy approach (rub with oil, bake to polymerize) using flax-seed oil. I have to say that the flax-seed oil gives a very strong coating. Nearly impossible to remove from the sheet pan I used to catch the drips during the oven 'cure'.
If I have a complex-shaped cast-iron item (grill, back-side of skillet) I use the flax-seed approach. If I want to simply build up the coating on the inside of a skillet, I cook the bacon. Always a good excuse to cook up a batch of bacon.