I think any one of those can work. Even on bitcointalk.org forum there are still scammers that will never pay you for the job you do. So if you find a manager that posts to their website and they are legit, then you can go for it instead of taking the risks with what you know nothing about. But first, before you start trusting any bounty manager and start working on their website, even on bitcointalk.org here, you should get to know about them and see if they paid for their past works, if they did, then you can go ahead with it and if not, then run as far as you can and avoid them.