A few comments:
Diamond Audio has great drivers...but the company itself is suffering right now....I honestly don't know if they'll still be around for a long time so...be cautious.
Image Dynamics: The idmax has been on back order for almost 8-9 months now. Don't get the IDMAX unless it's a version 4. The previous version had design or parts flaw. The V3 had problems with the glue bubbling up causing the rub in the coil. Hopefully...according to Image...the v4 will fix it. My experience with the IDMAX has been good...but they're fragile subs.
DON'T Forget:
The Crystal Comp subwoofers. Many have won SQ competitions with them. Also the price is very cheap!!!
Aslo, the new Eclipse aluminum with TC Sound's LMT is a nice SQ driver. I haven't tested the durability of these woofers yet though.