Avoid the silicone Fender Ashbory strings, they snap if you think about beer (or cheese, or elephants) within fifty feet of the thing.
I haven't tried the Thunderguts on a fretted ubass (they are on my Ashbory though). I have tried Pahoehoe polyurethanes; they are quite acceptable, at least to me. They do take a little while to settle down, but after that they last for years.