You must do you own research if you have some time, read white paper and learn the project, what it does. Also look for high ranked managers as they are more experienced in choosing good bounties. To be honest a lot depends on your luck, here is a good google web with all new bounties, for you to choose easier: https://docs.google.com/spreadsheets/d/1CiQRYU3JJyUnekC77DCG_7OgVUCeZy9l9KLaCaEwSik/edit#gid=0 , look for ratings, managers and then if you are interested read white paper, that's all