There are a fair number of bounty management companies out there now, and on this forum itself you can find bounty managers that run several campaigns themselves. You might be able to ascertain the quality of the projects simply by the management of their bounties, assuming you would trust the reputation of the managers.
AmaZix is one such firm with a proven track record of bounty management for some of the biggest projects since last year. Check out the official thread here on bitcointalk:
https://bitcointalk.org/index.php?topic=3308895.0It is managing many ongoing bounty campaigns right here on the forum too, feel free to check them out.
Of course, as user butka above says, there are many others to choose from but it's important to make sure you contribute quality to improve your chances of potential earnings - in fact, quality is something AmaZix prioritizes, as it maintains high standards for all bounty campaigns.
Good luck!