I've been thinking about this same question for my g/f's car. I have a Q and love it. It is very accurate (not quite as accurate as my brothers 15 tc2000) gets loud. (louder than the tc2000) especially at higher frequencies, and is reliable. Now one thing to think about is that the Q has been out for a while and there hasn't been any major issues, and I know they stand behind there woofers. I'm sure SSA stands behind theres, but personally if im gonna shell out my hard earned money, I would go with something that Is tried and true by many people here. You wont be disappointed in the Q.
P.S. I can only speak for a speaker that I have experience with