Question: what is the best 12 inch subwoofer to buy?
Answer: Best Overall. Rockford Fosgate P3D4. Rockford Fosgate tops our list due to its great sound quality and bass response. ... 
Best Value. Planet Audio AC12D. The AC12D is one of the best cheap 12-inch subwoofers available. ... 
Honorable Mention. MTX Audio Terminator.