Arguably the /peak/ of the franchise. In terms of the original 4 games (which was meant to mark the complete story) FNaF 2 stands as not only the best of the format, but frankly, the height of the storyline. This was before any revisions, any weird sci-fi crap, any convolution and plot holes. FNaF 1 started the franchise, but FNaF 2 was what gave it it's name. For good reason.

If you play any FNaF, just play 2. It's the scariest, it's the most interesting.