F tier - cops, military officers, coast guard, Immigration and custom inspectors
F+ tier - DAs, military, TSA officers
D tier - doctors
D+ tier - psychologists
C tier - nurses
B tier - teachers, private defense attorneys, tax collectors
A tier - social workers, janitors, government agency workers (DMV workers, office jobs, etc), public defenders, pro-bono defense attorneys
S tier - postal workers, firefighters, sanitation workers, veterinarians, anesthesiologists, park employees, forest rangers
Rest in Power p.a.t.c.o, martyrs in the fight for labor rights
EDIT: I'd like to add that this is mostly US-centric. In other countries, doctors probably range from B tier to S tier. As for defense attorneys, I honestly don't know enough about their demographics to determine how many of them are Alan Dershowitz and how many are actual public servants.
Workers that deliver significant benefits to society? I wish there was more employment for new grads in my field even though this would depress wages in the long run.
I would also note that single payer doesn't remotely mean the sorts of reforms that would actually ensure everyone has access, and I'm not sure the price gouging that goes with Medicare wouldn't similarly occur if its dreadful model was expanded.