Final answer:
Personal Appearances would be the most useful source, while Radio would be the least useful source.
Step-by-step explanation:
The most useful source for a candidate message would likely be Personal Appearances, as it allows the candidate to directly engage with voters and create a personal connection. This can help build trust and credibility with the audience. On the other hand, the least useful source would be Radio since it has limited reach and effectiveness compared to other media channels, such as television or social media.