Depends on what the car is used for. OBD2 is more advanced and will allow the driver to know more about what is going on with the motor because it has more sensors. Also, the OBD2 code is based on logic, so it will learn proper injection, timing, etc for maximum efficiency.

OBD1 is better if you are looking for some extensive modifications because it is chippable and doesn't use logic, so it can be easily manipulated into what you want it to do.