Subwoofer placement - back or front of room?

Or does it really matter?

Presently I have a 12 inch subwoofer located in the back of the room. In light of the nature of the waves being spread throughout the room I'm trying to figure out if moving them to the front of the room might be better or maybe it doesn't make any difference.  My main speakers don't have a problem creating bass so it's not like the room will be out of balance and maybe front loading all bass creation at the front of the room might not be such a good idea.

It's hard moving the subwoofer all around so this is an important decision.

Ideally maybe it would be Best to suspend the subwoofer from ceiling pointing straight down - wonder if that's ever been done before?