Margo,

To be a fully rounded guitarist, you need to be able to play both ways with equal facility. Either method, used exclusively, will tend to lock you into certain ways of playing and prevent you from playing a lot of really nice music.

If your banjo playing includes three-finger bluegrass techniques, you will want to be able to use your thumb to help with some chord patterns above the fifth string peg.

On guitar, if your goal is to play chords as an accompanyment to folk songs, just make them any way that feels comfortable and gives you the necessary speed. If your goal includes some measure instrumental virtuosity then you will want to master both left hand techniques and a number of different right hand techniques as well.

While you are under the guidance of an instructor, don't be too assertive in suggesting appropriate technique. Work to learn everything the instructor has to teach you, then use as much of it as fits with what you want to play. You may eventually outgrow your instructor and want to find one who can expand your vistas even more.

Good pickin',

      - Mark