I tried some Rotosound Nexus on my fretless and love them - they're not very durable when played with a pick though, so that might be something to factor in. The tension is great - almost the same as my usual 45 - 105 round wounds, the tone is bright enough to not sound like flats, and the string noise is reduced, but not too much.
I suppose it's a trade-off between string noise and brightness.