Everyone has their own tastes when it comes to cocktail hour. If you want some advice on this topic, it's all about volume levels, variety and mellowness. Keep the songs mellow and of many different genres (2 or 3 songs of a genre at most in a row) and have the volume levels set so that people can hold a conversation without shouting. Here are many different songs that work very well during the time when people are waiting for the bridal party to get done with photos or for dinner to be served.