The ideal size for the subwoofers is typically the size your vehicle has to spare. Some vehicles are spacious enough to handle the large-size subwoofers, while some are small and can not let you have the heavy stuff. Generally, the large subwoofers offer the best quality sound, but this does not apply all the time. Most of the time, the subs with the best enclosure are the best ones in quality. So, it is better to look for speakers in size acceptable to your car but come in the enclosure. If you find the one with an amplifier combo, nothing is better than that.