At this resolution, the 2 lower ones, the arches, don't really look different unless you really look closely. For them to work you need a much higher resolution-larger size or the arch needs to be a different color or texture. The narrow wall with pillars suffers from the same problem, though not as much. The only one that stands out is the opening.
My preference would be Narrow Wall with pillars, but with the narrow wall a different color. Then, if it is supposed to be a secret door, you leave the wall color the same as the regular walls.

Those dang copyright laws, always getting in my way... Thanks anyway.