Not knowing anything about what you are in search of is like walking in the streets blindfolded. You won't know if what you have is the one you need. With quality of course comes with a price tag, and you probably need to ask yourself the question of how much you would want to spend on your speakers best shallow mount subwoofer is an excellent resource for this.
Right off the bat, there are plenty of brand names out there that provide quality speakers, but you should always go to the showrooms to have a real live experience to see which ones sound best for you. In car speakers, the high end ones really often do demand a higher price, so you would most definitely hear the differences between a budget speaker and a high end speaker.
At the same time, especially for subwoofers, buying the bigger speaker does not necessary mean the better sound. A big subwoofer is not able to recover fast enough to produce the next bass hit. Having this in mind, you can start your search for the good subwoofer brands that are dependable but not really costly. Unless you need the hug speakers because you want to party each time you find time, consider the type of lifestyle you have before anything else.