The peace dollar is a challenge. You have to look at a lot of coins before you start to feel comfortable with the series. For me it is the Washington Quarter.
Without a doubt the toughest coin to learn to grade is the Washington quarter. And that's not just coming from my lips, most professionals will tell you the same thing. The design's lack of detail, even on fully struck examples makes grading them accurately a nightmare. That said, any coin that you are unfamiliar with is tough to grade. But that's because grading any coin requires extensive experience - with that coin. Example - I agree that the gold Indians are tough for most people because they have very limited experience with those coins. But gain the experience and you can grade one in a matter of seconds just like any other coin. But that is because the design has fine/intricate detail by which you can gauge quality of strike, lack of detail due to wear, breaks in the luster - all of the things you use to grade any coin. But the Washington quarter, that one has virtually no intricate detail in the entire design. Sure you can see breaks in the luster to judge if the coin is MS or not. But even a fully struck example, when placed side by side with weakly struck example, looks much the same. And for that reason MS examples of Washington quarters are graded almost solely by quality of luster. And that is one of the hardest things there is to learn about any series and it requires significantly more experience to do so. And when you get to the circulated coins, the lack of design detail on even MS examples makes it even harder to judge accurately what grade a circ coin may be, for all but the lowest circ grades. So in these cases the amount of remaining luster plays a larger part than it does with other coins.
So very much this. In fact, I'm going to have to start a "help me!" thread for my first quarter eagle -- I can't see any wear on the design, and there's plenty of luster on the design, but the fields are completely dull and lifeless.
Most modern coins are tough for me. Wash Quarters Roosy Dimes Franklin Halves JFK Halves Ikes There really isn't any reason to grade them once circulated. Good and EF are the same price on most of them except 32- D/ S quarters and there is little fine detail on any of them.
For me it's AU/MS morgans. I can grade coins below AU, coins I know are AU, and coins I know are MS, but I can't say if a coin is MS or AU.
I have problems with silver Washington Quarters and Peace Dollars for the same reason on both. They both have that weird white-ish luster that tends to make the duller coins in better condition have less eye appeal than the sharp coins in lesser grades. To a certain extent, the same happens for me with Franklin Halves. Some coins from the Middle East give me similar fits... but that's because I can't read what they say, so I'm unable to discern sharpness.