Id say the best out of the 3 is the Ti, but it costs almost twice as much as the other 2. the Ti will sound awesome, and be the loudest up to about 1kw. the x.xx and the IDMax are pretty similar in both SQ and output... The IDMax will do more with less power, and will sound better at lower volumes than the x.xx. the x.xx will handle more power, and still sound quite good, especially at higher volume.
The X.X.X. is the loudest sub out of the 3, and has fantastic sound quality. I use a 12" ID max v3 right now, and yes on the dream system thread I was referring to the V3s. For sound quality, It's right up there with the X.X.X and Ti, I like it a little better, that's just my preference though. It's not quite as loud as the Ti and X.X.X., but that's really not what I'm after anyway. It really shines in the midbass transition area, it's very clear and precise in that area, and is still extremely good down low. Erik, Seas makes excellent speakers, the Lotus drivers are very good, and Morel is extremely good as well.