I recommend getting something that is 60% cocoa or more.
The liqueur you choose depends on the taste you're looking for. Since Cointreau is from the town in which I lived in France, Angers, I am partial to it's strong orange flavor.
This recipe makes about 50 scrumptious super chocolatey melt-in-your-mouth treats.
Hint: Gently shake the truffle after you roll it in the cocoa, too much cocoa powder can leave an itchy sensation in the back of the throat.