As a reference, read here: https://bitcointalk.org/index.php?topic=3571218.0

But honestly you can make up your own criteria and standards of choosing a bounty campaign. Since you are new and having difficuly in choosing a "right" bounty for you, I suggest to read other thoughts so that you may have reference.

If the link above might not enough for you then do web search to your favorite search engine about your concern with the tagged "bitcointalk".