A non -200 737 rating will give you 300-900 on your license, in essence both classics and NGs.
However, if you train on one and then go to fly the other you need to do a differences course, I would say it's easier to go from the classic to the NG rather than the other way around - the improvements are easier to adjust to rather than learning the limitations of the classic (and the electrics is a nightmare).
So if you're going to do a 737 course do a 3/4/5.
I'm not sure that there's any value in doing a -200 course.
Regards