Ana,

That's why I'm suggesting Sully's books. He seems to advocate the most suitable style for any particular tune rather than focusing on a single technique.

I agree with some of CBs comments but would suggest the issue with changing keys is something that is a limitation with the 5 string banjo, not any particular playing style. It is designed to be played with the drone string as part of the sound. Using a single string style is a way of accomodating this limitation, but as CB says, you may as well be playing tenor banjo.... it no longer has the distinctive 5 string sound.

But, there you go. If we wanted to play sensible instruments we could all take up the g*itar!