If you're referring to U.S. coins it's a race between the quarter and the penny.
Because the Mint made a laundry list of mistakes back in the 1960s that led to the near-disappearance of half dollars, the quarter has taken on the role of the most-used coin for larger amounts of change-making. Before 1965 any purchase that required more than 50 cents in change would be made with a half dollar, and possibly one quarter; now it's 3 quarters.
OTOH although it's not very popular the penny is probably the most frequently used for two reasons: First, the presence of sales taxes and "99 cent" pricing in the U.S. means that most purchases rarely end up in exact multiples of 5 or 10 cents. Second, the failure of the U.S. to adopt 2-cent coins (compare to the U.K. and the EU) means up to four pennies are needed for making change, the most of any denomination.
The most sought after US coin is often considered to be the 1907 Saint-Gaudens Double Eagle, which is a $20 gold coin. It is highly valued by collectors for its historical significance, design, and scarcity.
There are many sought after US Coins. All collectors have their own goals which include different coins. A most sought after coin for one collector may not be sought after at all by another collector.
1933 double eagle American
The Penny is used the most in the US.
The most expensive coin in the world is the 1933 Double Eagle US $20 coin which sold for $7,900,000
penny
Most of the colonies had issued coins earlier, but the first officially struck US coin was the 1793 Fugio Cent.
The only US coin that is magnetic is the 1943 Lincoln cent, it's made from steel.
The most commonly known women on a US coin is Susan B Anthony. She was pictured on the US dollar coin made from 1979 to 1981 and again in 1999.
Quarter a dollar (1/4 a dollar)
On most US coins, the answer is on the bottom of the coin on the head side.
To determine the exact value of a 1928 US dollar coin, a couple different factors would need to be taken into consideration. Most important factor being, the condition of the coin.
US pennies have never been struck in lead, so such a coin isn't a US coin and most likely would be next to worthless.
That date at the most is $3.00 retail in AU-58