What is the most valuable US quarter?

Quarters have been struck since 1796 so there are a lot to choose from. Prices are retail as of 06/2014.

By far the most valuable is a 1796 Draped Bust quarter, with a spectacular retail price of $1.4 million in MS67 condition.

For Liberty Seated quarters 1838, the first year of issue, can bring almost $169,000 in top condition.

The most valuable Barber quarter is the 1901-S issue with prices ranging from $4600 to $167,000.

A 1916 Standing Liberty quarter's values range from $2900 in G4 to $44,000 in MS67. There's also a 1918 over 17 "overdate" that brings $1600 in G4 to $273,000 in MS67.

Among Washington quarters, the only standouts are 1932-D and 1932-S. These start at about $70 in worn (G4) condition; the S mint issue tops out at $20,000 in MS66 while the D version hits almost $94,000.