Best answer I've ever heard on front vs down firing subs is that if you have kids, a pet or are in any way busy close to the subwoofer a downfacing one is preferable. Coz you won't break it that fast.
In terms of sound there is a bit of a difference, but it's more a personal choice rather than quality.
Positioning of the system far outweighs down/front-facing in impact.
Long vs short is a projection thing. Short will just come out of the speaker, you can sit anywhere around it and get a decent experience, but the intensity will taper off quickly. Long projects more in a specific direction so that you can get listen to it far away (in the right direction), but sitting at half the distance to the side you won't get nearly as much from it.