John,

With all due respect, you've got it backwards. Listen to different kinds of banjo music until you hear the sound you want to duplicate and then get the type of banjo that is used to produce that sound.

Some banjo players use four string banjos and some use five. The styles of music are quite different.

Dwight Diller will be in Gainsborough in November if old time banjo is what you are interested in. See http://www.dwightdiller.com/pers/DDitin.html

If you want a four stringed instrument that is easy to play, try the Appalachian/lap dulcimer.