It comes done to what you want to achieve. If you want them to blend in to your surroundings, and you have bookshelves, place them there. If you want them to be accessible and in the open, do that. You are not mandated to do anything after you purchase them.....except enjoy them!
Your room and decor may dictate where and how they can be placed. As the other post mentions, the optimum sound will come from mounting them at about the height of the listeners position. It comes down to listening position and sound, balanced by what is feasible for you.
My advice would be to stand mount them. That is of course if these will be more than simply for background music.
Regards,
BBIBH
