“Internally”, a good portfolio is that one that shows something different. Your technique doesn’t matter at all; photo-bashing, 3D, full painting, etc. Nothing is better than the rest. Fresh ideas with bold compositions and vibrant lightings will always win. A good way to improve that is to enlarge your range of inspiration sources, and to not base your work only on other concept artists work or in a bunch of video games. Study classic art, watch (good) movies, read and learn from reality.