active is not necessarily better, but it can be.
active, as poida mentioned, allows tunability (presuming your active xovers have the appropriate range of freq settings), gain setting for individual speakers, and avoids some phase issues created by passive xovers (although that should be compensated by their design). however, depending on the quality of the passive xover, there may be no benefit with active in terms of SQ; dynaudio recommend sticking with their passive xovers with their splits simply coz they believe they're as good as you can get, perfectly matched for the speakers.
active can be expensive, consuming one channel per speaker, and sometimes necessitating buying a separate outboard active xover plus all its attendant wiring.
if you mix and match speakers for your splits, then active would be the best bet. and if the passive xovers are cheap quality, then also consider active.
hertz make some great speakers. their hi-energy HSK splits are excellent value. i'm not sure what they offer above these though. phil is the man to get advice from though, he knows his products and what works for them. i believe he's setup several active front stages using hertz speakers with good results. including his own, which run hertz midwoofer/midrange, and morel tweets (until he corrected me, i thought he ran a totally morel front stage

).
fudbutter (formerly rhuben) has hertz midwoofers in his gf's car, matched with mtx tweets, and the SQ is awesome for their cost. seriously good, running off a hertz amp.
whilst the HSK splits are great, there are better splits out there for sure.
if you audition dynaudio's and the like, and they're in your budget, i doubt you'll want anything less. and with the dyn's, you might as well run them passively with their xovers and keep the spare amp channels for your rears.
critter runs the S12L7 off the one JL 500/1.
whatever the case, i think with your JL amps and proposed setup, it allows you to expand later without losing out. so you could set it up as a simple system (albeit top quality components) to begin with, then if you're not happy, build on it. say, add a separate 3rd amp for rearfill duties, then run the 300/4 amp for an active front stage. even add a midrange for a 3-way setup. lots of possibilities.

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