If you have decided to have an open bar at your wedding, chances are you are trying to decide which liquors for the bar to provide.  More than likely, your caterer or bartender has a list of liquors to choose from in various categories.  The three most common categories are well, call and top shelf (sometimes called "premium").  Unless you really want a quality bar and it is a cost you are willing to absorb, most top-shelf liquors are completely unnecessary for larger receptions.  Your liquor bill is going to skyrocket, even if your guests don't over-imbibe.  Likewise, saving money by only using well is perfectly acceptable, but your drinks may suffer.  The best bet is to have a good mix of all three categories.  Use well vodka and rum, because it will be the easiest to mask in mixed drinks.  Save top-shelf for whiskey, and use a mid-range tequila.