What years are the most valuable for nickels?

Nickels* have been struck for about 140 years so there are many different ranges of value within each type.

The most valuable of all is the 1913 Liberty Head nickel, an unauthorized strike that has sold for millions. However, all pieces have been accounted for and are in museums or private collections. Below that few nickels are worth more than a couple of thousand dollars, among them the 1880 Shield type and several error varieties of Buffalo nickel. Please see the links below.

(*) FWIW, the coin is a nickel rather than "nickle"