You haven't said what your requirements are, so it's hard to go past offering the few differences between them. You would just have to make your mind up what's important to you. Those threads offer the differences. Decide what you need and get the one that meets those needs.
The specs are better on the FBQ than for the BFD. It's debatable whether those specs are significant for sub only use.
The BFD has multiple memory slots for different sets of filters rather than the single slot that the FBQ uses.
The FBQ has wider divisions between its frequency settings as the frequency increases, but again is quite suitable for sub frequencies.
The FBQ is a bit more expensive than the BFD.
The BFD is sometimes hard to find as it is being phased out (or once was anyway).
Some older stock BFD's still have the V1.3 firmware which had a midi bug that was repaired with the V1.4 firmware, but these are easily upgradeable. many don't even use the midi as it's easy to enter any filters by hand.
I don't know what more can be said...........
brucek