I think it depends on the difficulty. If it has a lot of tasks then better prizes especially if decent scores are required for the mini games. If you want a lot of people to play but don't have a lot to give away, you can always put pixels or other throwaway prizes after you've given top 5 or 10 good prizes so people can still play for the fun of it rather than for prizes. PM if you need more suggestions and I would be glad to help out.