Firstly evaluate the project in which you wish to participate, because if this project has no worth for community, even the biggest bounty pool will not help. Token you will get for bounty tasks will cost nothing and your work will be in vain. If project is interesting - so pay attention at the amount of participants, duration of program ( the shorter the bigger reward) and the pool.
I like to join the bounty program with shorter time of ico. We could not really measure to get high invome from this but we can do small check before joining the bounty to reduce our chance to fail in the project.
For me, shorter time of ico make us getting our reward quicker.