Which is the better woofer?

I am well aware the second woofer is much more efficient, but in every computer-based simulation of low-end frequency response, it has a much, much higher dropoff, creating pretty crappy < 40Hz response. And it's 6 ohm. So I ask, which is probably the better choice, and why?

Pioneer A25FU14-57F:
Outside Dia: 256mm
Impedance: 8 ohm
Power: 70W
Freq. Response: 28Hz - 2.5KHz
Magnet: 14Oz
Fs: 28Hz
Re: 7.4 ohm
Qts: 0.49
Qes: 0.55
Qms: 4.28
Vas: 121.2 L
Xmax: 3.4mm
Voice Coil Dia: 38 mm
SPL: 89dB
Depth 104mm
Baffle Opening: 236mm
Mtg. Cntr: 248 mm BC x 4

Pioneer A25FU30-51D:
Outside Dia: 256mm
Impedance: 6 ohm
Power: 85W
Freq. Response: 26Hz - 2.5KHz
Magnet: 30 Oz
Fs: 26Hz
Re: 5.5 ohm
Qts: 0.20
Qes: 0.21
Qms: 3.36
Vas: 171.9 L
Xmax: 2.9mm
Voice Coil Dia: 38 mm
SPL: 93dB
Depth 113mm
Baffle Opening: 236mm
Mtg. Cntr: 248 mm BC x 4
I ran some numbers through WinISD, and got some answers for you. The A25FU30-51D driver is NOT for you. It's -3dB point, in an optimum configuration is 73Hz, but can be lowered to 46Hz, by using an EBS (Extended Base Shelf) configuration (for more information on EBS configurations, please see 'http://www.diysubwoofers.org/'). The response falls like a rock below that. If you're using a sub, this might work out, but you didn't say.

The A25FU14-57F should work for you in either a sealed or a vented configuration. The vented configuration (limited to 120L, to accomodate the port, and stay within your limits; it thinks it wants 300L) shows a -3dB point of 29Hz. The sealed configuration (Qtc=0.7) shows a -3dB point of 40.5Hz, but with slower rolloff than the vented.

The room acoustics must also be considered. Most rooms will give a 10-20dB boost by 20Hz (smaller rooms give higher boost). With a vented enclosure, this would probably end up sounding boomy.

I'd go with the A25FU14-57F in a sealed enclosure, between 120 and 150L. This should give fair results. Please note, you will not be able to get loud, low bass out of this driver (at least not and have it continue working :D ).

FYI, sealed enclosures are the simplest to build, and the most forgiving of minor math errors (size).

Good luck.