Should Pickle Slices be Above or Below the Hamburger
As you might guess there is not hard and fast rule for this.  It depends on when you want to have the flavor of the pickle hit your taste bud; before the savory or after the savory (meat).  Additionally it could be complicated by other condiments you have mentioned above.  However there is a bit of science you can employ here as well.  Pickles (assuming you are using dill) activate the sour taste buds in our mouth.  Savory (umami) is not as widely distributed as sour. So from that standpoint if you really like that savory flavor from a freshly grilled juicy burger, you would want to put the pickles underneath the meat.  If you prefer the pickle taste to be front and center place them on top.  I've included a reference for you as well.  Happy eating! http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072592/