For my money, it's Nordstrand all the way. But that's only but so helpful, because it's your money, isn't it?
There are several threads that compare the two, but in short, a lot of people view Sadowsky as a 'modern' Jazz, whereas the Nordy is more true to the vintage sound/feel. Beyond that, you really just need to try at least one of each to get some representation. The good news is, since not everyone can easily do that, you're going to get a great bass, whichever you choose.
To me, Nordys and Sadowskys sound very different. Largely due to Carey's pickups, a standard Nordy sounds fairly vintage, with a good bit of midrange content. A Sadowsky, on the other hand, has deep bass and lots of sizzly treble, but definitely scoops the mids to give a more modern sound. I also prefer the Nordstrand preamp; it's much more adjustable, whereas just a little bit of boost in the Sadowsky preamp gives a dramatic change in sound, and that can be hard to control.
Anyway, that's my take. Good luck!