I can probably help with this. Depends on what you're looking for though. In SPL, the Cerwin Vega's will prevail and deliver good SQ. The Diamonds will deliver high amounts of SQ but withouth the SPLs.
I personally am what you'd call a suck for Cerwin Vega lol. And which VMAX's are you referring to? The old 300W RMS 12" model or the new 600W RMS 12" model? I tend to think the VMAX's are a bit underrated, but that's MO. I myself am purchasing the new model VMAX's this winter.
However, the Diamonds will still have the greater SQ most likely, but the SPLs will not be matched.
Cerwin Vega and Diamond are far better than those Pioneers, so whichever you choose, you will be much happier with.
Overall I would say the CV's are the most well rounded sub with SQ/SPL. It really depends on you more though, what's more important, SQ or SPL?
Bad as in good? Then yes, the new Vmax I'm sure has greater SQ in light of it's new found power output. Honestly, I think you'd be happier with the Vmax.
Just make sure you get the new model. It should be more widely available in a month or so. They have them on E-Bay sparingly right now, and SOME on Froogle.com. Have to search a bit, but they're there.
Ah, I don't think the Pioneer's are even a question. They're no match for ANY of the speakers you mentioned above, as they wouldn't have the SPL or SQ of them. IDQ's I'm not all that familiar with, MIGHT want to ask someone else about them. I've heard the IDMAX's are supposed to be thought of by some as the best all around woofer. So the IDQ I'm sure is good too. Just ask around about that one to be sure though, as I'm not that familiar with them.