It always comes back to the instrument. I heard it said a long time ago that a great bass is one that sounds good with the least amount of electronic intervention: it should sound good passive and EQ set flat. Then things like preamps and amp EQ are just there to tweak the sound.
Granted, things like preamps can make a not-so-good bass sound better, but if you need to make radical EQ adjustments via preamp or amp, chances are you really need to find another bass.
Anyway, a musical instrument is organic - all these components: tone woods, neck/fingerboard type, strings (new, old), pickups, etc. -- if a certain preamp rocks your world, it's probably probably because it's in synch with all the other ingredients that combine to make that wonderful sound you're loving. Which is why we bassists keep mucking around, swapping pickups, preamps, trying every string under the sun, etc. -- looking for that right combination. It never ends!