Need a little more information on what you have - size and shape of tank etc. However, the one that seems to promote the best circulation is the 2 seamounts. Just keep in mind some basics for the design:
Be creative, it is your design.
Make sure there is good circulation around all structures
Don't stack the rocks against the back wall - creates dead space]
You already recognize - make sure the structure is stable
Stack the rocks firmly but not densely together, make sure there are lots of openings for water to circulate through. HTH