down firing or front firing sub?

Downfiring gets the maximum room loading/efficiency and minimizes the audibility of higher harmonics (due to distortion).

I tried my Rega Vulcan downward, frontward, backward, sideways, ... found it worked best for me in my room firing backward with the cone alligned somewhat with the plane the rear port of my mini monitors are in...
I would say play around and see what happens.. I have my sub sitting on 3 walker cones going into a rug. Not using the feet of the sub itelf.

Down firing is better for music because it blends more seamlessly with the main speakers.

Forward firing is better for HT.

Down firing, because I can simply turn it upside down and put a weighted board on top and achieve much better performance. With a front firing sub you would have to raise it up on blocks or something to get it off the ground.

It depends on the application. All good points above, but, in some instances front firing sub(s) might have some advantages. Those that have neighbors below them, might find front firing subs more suitable. So might those that might not have the firmest flooring. In the near field a front firing sub might offer better driver integration with the main speakers.