for dividing the midwoofer and tweets, passive is often better (and more often used) because the values are usually set and cannot be changed. this is important because the relationship between the crossover points and the drivers is important to the overall response of the speaker system. you don't want to make adjustements to this relationship unless you know what you're doing. it's usually best left to the speaker designers.
passive crossovers are also cheaper, smaller, and easier to install than active units.
on the other hand, active filters can be better if you have the extra money and the time/knowlege to tune them correctly. actives also have the advantage of being very efficient. while passives waste a little power being on the output side of the amp, actives do their job upstream and are powered, so all of the amp's power is utilized by the speakers.
for dividing components and subwoofers, i always prefer active crossovers to passives because of the ease of adjustment. since the components and sub systems are rarely matched anyway, it's beneficial to be able to experiment with different values until everything sounds right.
one of the few downsides to actives is that they can be bumped or touched by curious individuals. it is very easy to mess things up and not be aware that something happened. audiocontrol has remedied this problem by requiring the use of programmable modules that cannot be tampered with or "bumped". you can build the modules yourself, so they are entirely customizable. they're not for everyone, but i use audiocontrol in my system because they do what they are supposed to and never give me problems.
to answer the question, it's probably best to use a combination of passive and active crossovers in your system. use the type that gives the best advantage for a particular application.
Adding to that, the only real benefit (if you were to compare the same passive with an active crossed over the same) of a passive crossover is that the designers have compensated for impedance curves of the driver, usually via Zobel networks. Other than that, active offers the best performance of a driver. I don't understand why manufacturers don't offer preset active x-overs that you could plug in-between your RCAs and your amplifier. It would make sense. Maybe that's how I'll make the big bucks one of these days
