Reverse osmosis would be ...

Reverse osmosis would be very effective at reaching specific levels of TDS but you would need to consider the potentially higher cost of running RO equipment (replacement membranes as well as operational energy costs).

Also you would need to consider what to do with the reject water, which would have a TDS value of several thousand. Discharging to ground could eventually contaminate your aquifer, whereas discharging to a water body (river, lake, etc.) would likely cause environmental and ecological problems. Some of the reject water would be blended back into the treated water, in order to raise TDS back up to 200 ppm.

I do not have professional experience of EDR, but my initial research suggests that it is primarily used for brackish waters (i.e. TDS of several thousand). Perhaps it might not be as effective as RO for reaching 200 ppm? Although I would be happy to be corrected by an expert in EDR.