Subwoofers - Front Firing or Down Firing - Which Sounds Best?

     Since I use physically time-aligned B&W 803's, I have my subs positioned to be in phase with the main speakers.  To do this, I measured the center of the B&W magnets, which are all the same, and the subs, then measured where to place the subs.  Of course, I then had to determine whether to place the subs inside or outside the speakers, and finally decided on under them. It worked the best, largely because my speaker room floor is several inches lower than the living room into which it is open through a 12' x 14' hole in the wall (Actually, a lack of a wall).     Otherwise, I would have to use a high chair, but I might just have done that, but probably would have kept them between the speakers.

I find down firing subs are good for 
Home Theater and Front firing subs 
are good for two channel music.

It depends on the driver. Drivers with stiff suspensions can fire downwards fine. Those with looser suspensions are better off front firing as they may sag mounted downwards and the driver becomes non linear. Given a driver that can go either way there is little if any difference. More important is that the driver have one edge right up against a wall or corner. Then multiple drivers and finally room control. The radiation pattern of the sub should match that of the satellites. Point source speakers should have a point source sub system. Line source speakers require a line source subwoofer system. A Line source sub will dominate a point source satellite and a point source sub will get lost under a line source speaker. 

@shakira - Nice response! Simple, clear and to-the-point! I like that...

I have one set that is downward firing (a pair of woofers mounted face to face (isobaric on a vertical axis, vented laterally) and one set that is forward firing and find no significant difference between them.  It is more important that you have two of them than which way they point, IMHO.