The 5 string is used for Bluegrass music, usually in the style popularised by Earl Scruggs, and players look for a resonator and tone ring. For old time clawhammer or frailing styles, an open backed simpler model is better. Finger style classical banjo also uses the 5 string, but is less common now. Used for bluegrass and country music. But is also used for old time and song accompaniment in the British Isles.
Bluegrass players favour banjos with a resonator back. Old time players often favour the open back variety. Many tunings are used, especially in old time music, but the most common are gDGBD and gCGDB.
The long neck 5 string (almost always associated with Pete Seeger) is 3 frets longer than the usual 5 string.
The fretless instrument (often strung with gut or nylon strings) was favoured by some old time players because it allows the player to follow more closely the fiddle playing.
The 5 string was also used for jazz and earlier popular music.