Passive bass - active box. Active bass - passive or active box.
From the ones I've used it seems like you get a better sound from a cheap active box than a cheap passive box. Much depends on what you want it for - I use a sansamp a lot, but I often use it as an amp substitute or overdrive. I also use a radial Pro-DI (medium price passive) but this normally comes after a preamp send (to keep phantom power away). Both can/do sound excellent. You can easily over do the eq/emulation on the sansamp, so it pays to get to know it well (you can also switch it all off!)
Another thing I've learned - an active DI that clips (runs out of headroom and distorts) sounds awful, but a passive DI can be more forgiving. For a live situation, with a loud band, I'd prefer to use a good passive DI run from the amp.
Have a look at Orchid electronics - they have a cheap(ish) active design that I've also used for 10 years, and there's nothing wrong with the sound at all.
BB