I can field this - it really boils down to what you, and your guests, drink. There's no point in having a bottle of brandy if you're never making cocktails with it. Conversely, if you're a rum whore, having 2 or three rims of different tastes would be a great way to enjoy yourself. Buy what you like and build out from there. Always have 1 of each basic - vodka, rum, scotch, gin, tequila. Have mixers like various sodas and limes. And a few of each glass type, depending on the amount of people you have drinking - highball, rocks, martini (if you drink them) and any others you might use.