First things first. Think about your meal. For larger/heavier meals choose lighter desserts, like a French Vanilla or Peach. You don't want your already full guests to have an even heavier dessert. Rather than dancing the night away, you may find them slumped over in their chair ready to curl up in a warm blanket. If you are having a lighter meal, then by all means...go for that Black Forest or Italian Cream!
Second, think about your season. There are some desserts that are seasonal. If you are getting married in the fall, add that extra little touch to your wedding by choosing a yummy spice cake! Or maybe a Strawberry cake in the spring!
Lastly, think about your guests. If you are having a larger wedding or a wedding with lots of guests who you really don't know too well, consider something more basic, like a vanilla or butter cake. Those not only appeal to the masses, but you have less to worry about when it comes to allergies. You don't want to order a super tasty Italian Cream cake when 1/3 of your guests don't eat coconut and another 1/4 are allergic to nuts. If you are having a smaller affair or if you know your guests through and through, then think about what the majority will like. Are they choc-holics? Then maybe a German Chocolate cake might be a great choice? Or a chocolate cake with a Bailey's chocolate mousse filling...a favorite among my house!
But don't spend too much time stressing over this. Unless you are going to be on "4 Weddings", your guests won't be picking apart your wedding and critiquing every little thing you do. They will be there enjoying and celebrating with you and whichever dessert you choose, they will love!!