The $25 1991 Uncirculated Gold eagle has been considered the key date in the Regular Uncirculated $25 Gold Eagle series for many years. However, in 2006 the Mint struck a Special Burnbished Uncirculated version that has a W mint mark. These 2006-W Burnished Gold Eagle coins were struck with lower mintages than the regular 1991 $25 Uncirculated Gold Eagle. However, many collectors continued to consider the 1991 as a key date even more so that the lower mintage 2006-W Gold Eagles. This has also been supported by the fact that the 1991 $25 Uncirculated Gold Eagles still bring a much higher premium than the 2006-W Gold Eagles.