I didn't like Nylguts at all on my fretless banjos. I'd run Savarez "yellow card" strings on them because they have a matte finish which I think sounds better when doing slides, etc. I liked them so much I used them on fretted nylon strung banjos as well.
They don't make them for banjo as far as I know, so I'd buy two guitar sets and use the 1,2,3 and 4th string and the 1st from the second set as the 5th string. Since they typically last just about forever on a fretless, I could justify the added expense of buying the extra set. Of course, if you can find a source for individual Savarez yellow card strings....
