I personally prefer the 500K pots after having tried both on my Darkstar'd Jazz, but also tend to play without either of the volume knobs turned up all the way- so there is always more than just the 500K loading anyway. I like the percussive snappy quality I can get in spades with 500K pots- though this quality is already accented naturally with the Darkstars, so it may be too much for some people. My feeling is that the broad frequency response of the Darkstars is one of their main attributes, so I want to use electronics that allow those frequencies through as well as possible while staying passive (I had an Audere in mine for about a year, but it made the pickups a little TOO clear for me- until I improve my technique significantly, I'll stay passive with this bass!).
You can also experiment with different tone pot values to get a similar effect (you could even use 250K pots for volume and a 1Meg pot for the tone, so most of the brightness would be dependant on the tone settings)- I used 500K for all 3 of my pots, but I'm sure that would be too bright for many people.
Really it's all just a matter of preference, and most of the tonal differences will be negligible or recreatable more or less by using amplifier EQ...
Karl