When tasked with writing a literal essay, you organize your points in strategic order. You put the strongest points at either the beginning or the end of the essay and the leave the weaker points in the middle. By placing the strongest points at the beginning, you instantly draw in the viewer and grab their attention. By placing the stronger points at the end of the essay, you end on a high note, leaving the viewer with some strong points they wont forget.
Its the same with your photography portfolio. If you place your strongest images at either the beginning or end of the portfolio, you will hit the viewer the hardest. I recommend using both ends of the spectrum, grab their attention right from the beginning and leave them something to remember at the end of the portfolio.