I am currently testing out primedice's campaign so I will tell you guys how that goes by the end of the term. If you post a lot primedice definitely seems like the most valuable campaign to invest in, because if you post 400 times a month as a hero member (if you post that much you probably already are a hero member), you can make 0.48BTC a month, which is a heck of a lot of money.
We could debate alot on "heck of a lot of money." , but its not something to ignore either.
Previously you could earn 2,4 btc/month, which was much better, and then spammers came and ruined everything.
From my experience i can assure you that you will get paid, so you dont need to worry about that.
Cheers