Deering makes the finest 17-fret and 19-fret tenor banjos today. Tenor banjos are 4 string banjos that are traditionally tuned in 5ths (C,G,D,A - standard tuning, G,D,A,E - Irish tuning). These types of banjos are traditionally used for either Traditional New Orleans Jazz or Irish music.
The 19-fret tenor banjo is the most common because it gives the banjo a larger range. The 17 fret has a smaller scale so the frets are closer together, making it easier to play quick single note passages or large chord shape stretches.
Both banjos can also be tuned to Chicago tuning which is the top 4 strings of a guitar (D,G,B,E). Learn how to choose the correct strings for this tuning here.