AvatarNathan Richer

of the 3, ART and Graston fall into one group and chiro is another.

ART involves the use of your limbs/hands/fingers to massage you and take out knots and kinks through manual manipulation.
Graston is like ART, only these practictioners use stainless steel tools to scrape out knots and problems in fascia and muscles. 
I have found that ART can get deeper into muscles for problems, where Graston cannot reach. I had some great work done on my psoas – it was the most painful thing having someone drive thumbs along my pelvic bones! but man could i run more easily after that happened.  certainly a good practictioner can sense problems with their fingers as they probe you.
However, I know of a Graston person who did magic with her tools. I had never met anyone who could rid my body of problems like she can. There is a sensitivity that you develop over experience and time with the tools so you can sense how hard to scrape, where to scrape, and when to stop.
Chiro is more about adjusting the joints and putting them back into the right places. I have met good chiros and bad chiros. Some don’t know when they should NOT adjust you and make a problem worse. Some simply don’t even know how to adjust certain body parts, like the ankles or toes, or how to put a rib back into place.  your joints can get out of whack over time, or back out of whack after exercise. it is a good idea to find a good chiro to make sure your joints are properly aligned on a regular basis.  certainly some MWOD work will do this for you also, but there will be some adjustments that you cannot effectively (or safely) do yourself.