For my apple pies, I use a combination of Granny Smith apples and Honeycrisps. If I can't find Honeycrisps, I'll actually use all Granny Smith apples because they're on the tarter side and have nice snap which doesn't completely disappear while baking (there's nothing worse than a mushy apple pie). But not everyone would agree.
Last week, Melissa Clark posted a video on The New York Times detailing her favorite apples for pie. First she describes apples you can find in the supermarket: Granny Smiths are crisp and tart, Golden Delicious are crisp and very sweet and Macintosh are soft and mushy but "in a good way." Then she moves on to farmers market varieties like Jonagolds. In conclusion, Clark says to just mix them up. Buy as many different kinds and varieties as you can, slice them all up, and you'll have the best of all worlds.
(Image: Megan Gordon)