Simple and traditional, for great old-time tone.
Here's a well-made example of one of the earliest banjo tone ring designs: an unplated brass hoop, .273" round in cross-section, that simply rests on top of the banjo's wood rim. Uncomplicated yes, but the workmanship is impressive: it's nicely fabricated and lays flat, allowing more consistent banjo head tensioning. A great choice for a traditional old-time banjo sound, in 11" and 12" diameters.
"They are great! Good weight, diameters are right on, and they are flat! I will be using them exclusively." —Will Fielding, Fielding Banjos