What are the reasons for choosing one 5-string banjo style over another and which styles suit which types of music?

"Style" really isn't the right word to use for this. You are a lot better off thinking of the various ways to get music out of a banjo as techniques.

For example, I use the technique called frailing. I can take that technique into bluegrass, slide blues, country, folk songs or any other "style" of music I choose.

I can do this because I stuck to one technique long enough to get really comfortable with it.

It is easy to do a lot of things badly. It takes discipline to do one thing well.

-Patrick