This is a tough call but I've heard w6's and I just got my dad an image dynamics ID12D and I was really impressed with the sound of the ID. I would probably give a slight edge the the image dynamics.
I dont think you can go wrong either way. I own both and love them both. If you already have an amp, let that be your deciding factor since, unless something has changed, I think w6s are still only available in dual 4 ohm configuration, while the IDQ can be bought in D2 or D4. If you don't have an amp, just buy whichever one you can get a better deal on, then find an amp to match.
new idq can be reconed in 10 minutes, not to mention it looks 100x sexier, weighs less, and from my recollection should have more xmax and potentially be louder than the w6.
the w6 has to be replaced.
on that alone, the idq wins hands down if you blow it or damage the softparts for some reasons (children, pets, golf clubs, ect)