I've never personally heard the IDQ's... but I'd say the IDQ's will sound a little better, but the W3's will get a little louder. Both are great sql subs IMO.
I have never heard the IDQ's but i have 3 12w3v2's and they sound awesome you will not be dissappointed w/ them. I can't imagine that the IDQ's would sound signifcantly better. if they sound better it wouldtn't be by much. the JL's are a very accurate sub
i haven't heard the IDQ's either, but i have heard the ID's, and i must say they are one of the, if not the most accurate entry level sub i have ever heard, and they get very loud with little amounts of power.
the IDQ's only handle about 100wRMS more than the ID's(read their PDF files on the tech page) and they have a significantly larger Xmax.
I have been widely researching the very same issue over the past wk . A 12" IDQ is 350wrms A 12" IDMAX is 1000wrms but can be normally powered comfortably around 800wrms which is still 100w over 2 idqs . A friend who has heard them told me the idmax is totally awesome loud with really great sound quality !
I'd give a slight SQ advantage to the IDQs over the ID Max at lower power, once you get into higher output the ID Max starts doing better. They're both very close to one another, though. Enough that the linearity and output of the ID Max makes it more than worth it.