I agree with many of the posts.
Resentments for me have a nuance of internal. Of stuffing, or festering of simmering of old stuff fermenting over time. I have had many I needed to work through in my recovery, and while often I get to them because of loving a problem drinker there are usually threads to long before he was in my life and often trace to childhood. I am actually having physical symptoms from some of these at the moment, and in the last three weeks in therapy sessions (and my training) am actually burping uncontrollably for hours on end. Then I start yawning. Very strange and has not been related to food but I think is about how long and hard I stuffed things. My resentments almost always have a sense of "I failed" in there somehow.
For me anger has been more external (only after getting some counseling). There have also been some physical signs/symptoms but more in the moment. They come up when a boundary (which I am finally learning how to set) is crossed. For me anger has been newer, cleaner and often I am able to express it and be done. It does not fester.
Having anger for me has been a sign of health. I have not gotten out of control with it and I express it okay.
Resentment has not been that way. I self-destruct, whip myself and use other unhealthy coping mechanisms.
Thanks for the topic. The nuances we all have been discussing has been great.