I once did a bounty that was paid in Eth, it was a great one but the issues was that we received very little and I believe it we were paid in their token we would have gotten a bigger profit
It all depends on which project you are joining and how much investor are supporting the project according to that they will value the coin in exchanges. Their are so many coins which were listed and then the price went high but after some time the price started to drop and then it never went up. So if you see in long term then you will feel that getting ETH payment in bounty is much benefits. Even bounty tokens are also distributed after some time of it get listed so till then the price goes down