When I choosing a bounty :
First, you should be project's research on product goals, roadmap, team, and advisors. Usually can be seen in the whitepaper.
Secondly, you can see the project community. If a strong community will usually have an effect on token sales.
Third, you can see the manager who handles the project. A manager provides an important role in a project. But it's not uncommon for unknown managers to have good projects.