There are a couple minor differences between the chips. First, there are the package types (physical size). The chip normally used in a controller is DIP package (stands for Dual Inline Package). There are other package types, but they are for surface mount on a circuit board, so you won't want to use that. Now, when looking at the DIP package 12f683, you will see two versions. At the end of the part number will either be I or E. "I" stands for Industrial, "E" stands for Extended, and it is referring to the temperature ratings the chip can handle. The Industrial type is cheaper and is more than enough to work in the controller. So, to sum it up you want the DIP package 12f683 Industrial rated.
