Dear all: I am planning to spend $200 something on a subwoofer. I came with the following picks:
1: Polk 10" Subwoofer (Black)  
Built-in powered amplifier: Bring your favorite movies to life with rich, full bass provided by the 50-watt RMS amplifier. 
40Hz-200Hz frequency response (+/-3dB): Get the full impact of your favorite movies with a 40Hz bass response.
2: MTX 12" Subwoofer (SW2)  
Built-in powered amplifier: Bring your favorite movies to life with rich, full bass provided by the 100-watt RMS amplifier.
35Hz-1600Hz frequency response: Get the full impact of your favorite movies with a 35Hz bass response.
3: Velodyne 10" Subwoofer (VRP-1000)
VAI   VRP1000B  
• 10" woofer 
• Front firing design 
• 115-watt RMS amplifier  • 50Hz-200Hz response 
• Line-level inputs 
 
Will you please tell me which one is better? Thanks for any advices!