Is there a particular U.S. series that you find the most difficult to grade? Mine is a toss up between Jefferson nickels and Washington quarters
I generally use PCGS Photograde for grading all my US Coins. There is an App you can download, or go here: https://www.pcgs.com/photograde/
Morgan dollars when friends ask me for a grade....mostly because since I've never had any urge to own one I have never had any desire to learn how to grade them.
Rosey dimes. partly because the obverse details are vague and partly because the coin is so small to start with.
The series that brought me to collecting. Franklins..... I have a devil of a time sorting out the grade on those.
Even among pro graders Washington quarters are often thought to be the hardest to grade. I'm inclined to agree.
Same here I have two grading books, Photograde and The Complete Guide to Buffalo Nickels by David W. Lange. I consider myself decent at grading buffalo nickels and I can take stabs at other series. If a person is going to specialize in one series, they really should have AT LEAST one book about it, IMO.