The MTX 9500's are great subwoofers. They are one of my favorite "main stream" subwoofers I have ever had. However, they are overpriced and if I remember correctly, they have gone on for years and internally unchanged. I could be wrong.
I think everyone has forgot to ask a very important question. What amp will you be running or are you deciding on your subwoofer first, then pick out your amplifier to spec?
I have noticed that you must have deep pockets, because the subwoofers you mentioned OP, are pricey subwoofers. So if that's the case, then I recommend a pair of SoundSplinter RL-S. They get loud and sound great doing it.
As for the TC Sounds, they are geared more towards Sound Quality. They have a different kind of sound. I have a pair of TC Sounds T1000's with the TC2+ motor sitting in my closet with a pair of my RE SE 12's, which brings me to another recommendation of the older model of the RE XXX's. I have read on the board that the newer XXX's arent as great as the previous versions. I dont know about this first hand, but seems to be the general consensus about the newer versions.
What vehicle will this be going in? Plan on going sealed or ported?