As of last year, Dark Horse stainless steel roundwound bass strings were the best surprise I had playing a model of strings that I never played before. The way that traditional single coil bass pickups can have a sponginess to their sound, these Dark Horse strings have a fizzy plus rubbery sound. Soulful, harmonically rich, spitting or twanging on demand, and planted. That's the best I can describe them for now. I fckuing love those strings. They are rare, though. Right now the Dark Horse website is not working, so they might stay rare for a while.
Also recently, another good surprise for me was Curt Mangan flatwound bass strings. I tried some on a several-year-old Custom Shop Precision Bass and really dug them. Then I tried a second set on a handmade J of similar age that I was using to test sets of pickups. The Mangan flatwounds were great for J bass (I kept trying to cop old Bootsy Collins lines). When I decided I needed roundwounds on that J instead, for testing pickups, I swapped its Curt Mangan flatwound set onto a 1969 Precision Bass. Wow. With those strings on it, I heard that bass's voice completely for the first time. Expansive, open air surrounding thick, holographic low end. Huge. Pure, solid pitch. So nice. To quote Sarah Silverman, "So yeah... that's a good cheese."
DR still makes some of my bread and butter roundwound strings (Hi-Beams, and nickel and s.s. Lo-Riders), but they lost some business to Dark Horse last year.