If you want to get high rewards. I think you should join in the Signature bounty that doesn't have any participant that join.
Or maybe the bounty that won't last long, like only 4 weeks. I'm sure you can get a lot of tokens joining on its Signature campaign.
If a bounty doesn't have any signature campaign participant, I think bounty will be extremely bad and maybe it's a bounty scam. I agree with your next opinion, choosing bounty for a short time. From 4-6 weeks to join, we will get more tokens