Microneedling or Medical Tattooing? Which would be the best route for reducing the appearance of my scar? (photos)

You pose an excellent and very tricky question. Microneedling especially with PRP has been found to be helpful in improving the appearance of scars. It is generally considered a very low risk treatment with the most common side effects including temporary skin irritation and redness. It may take multiple treatments to achieve the desired improvement and there is always the chance you could be underwhelmed with the results. Medical tattooing is exactly as it sounds. It is a tattoo that is placed for medical reasons, such as recreating the pigmented part of the nipple areola complex in breast cancer patients. This is a fairly permanent procedure, although it can sometimes need to be retouched after 3-5 years. Concerns could be that if you are unhappy with the result it is a more permanent procedure.
In addition, scars can change and improve dramatically on their own with time, and there are many modalities that can improve the appearance of a scar even outside of microneedling or tattooing. Finding a provider that you are comfortable with and would like to work with on this concern is most important. A board certified plastic surgeon or dermatologist who has knowledge of both procedures and understands how scars mature with time is a great place to start.