Every year we eagerly await the arrival of the Michigan apple crop so we can start making our fabulous caramel apples. At the beginning of the harvest we use Jonathan apples, a traditional variety that is tart and juicy. This makes a great contrast to our freshly made soft, sweet caramel. Topped off with chopped salted roasted cashews (made from the broken pieces we screen out of our colossal cashews), I think this is the best caramel apple made.
The Jonathan apple doesn't keep, so the season is only a couple of weeks long. We extend our production to the end of October by switching to a later variety -- still locally grown -- the Fuji. This apple is sweeter, and some folks like this better than the tart Jonathan.
Once the local crop is done, we stop making caramel apples. Plenty of folks use stored Granny Smiths so that they can sell caramel apples year 'round, but I find that the apples are usually tasteless and often have a dry, cork-like texture. (Paired with poorly made caramel and often slightly rancid peanuts, you often need all kinds of fancy chocolate coatings to make the things edible.)