This depends on your requirement and developing skill.
For deepstream-app sample, it is a c/c++ sample of dynamic DeepStream pipeline construction through configuration. DeepStream Reference Application - deepstream-app — DeepStream 6.1.1 Release documentation. Users can construct basic DeepStream pipeline with some fixed types of fucntions without any code. But some parts of the code may be redundant for the fixed scenario. And it is very hard for some users to customize functions with deepstream-app sample for the complexity of the code.
To summarize, DeepStream is just a SDK, all samples are for the demo of how to use the APIs provided by the SDK. You need to make your own decision for which sample to focus on based on your own requirement and developing skills.