OBDII- tougher to tune with(aftermarket parts) verse OBDI, but it is a more in depth diagnostic than PBD1 and easily available at most shops when you do have issues.

OBDII- has EECPROM OBDI doesn't, which allows you to tap into the memory and check the code history, also lets you know when, what,how, etc that the pcm has been reflashed, etc.