If you are the manager, you would choose the one that would help employees continue to work for goals and increase company productivity. In that vein, I would choose bonuses.
Raises are seen as a normal part of advancement in the company, and everyone gets one. This is a type of socialism. Socialism breeds the mundane. If everyone gets a raise, in other words, why should I work harder than anyone else?
Parties are seen as a "whim" of the boss, not tied to performance at all. Besides, you get what you get...no choice on how to use your part of the money. It's all spent on the party and everyone shares equally, much like the aforementioned socialism.
Bonuses, however, can be tied to the particular work ethic of each individual. And, the harder you work, the more bonus you may receive. I believe we call that capitalism.