I prefer bounty campaigns with fixed rewards because I know exactly how much I could earn.
While in stake based bounty campaigns you never know how many total stakes will be at the end of campaign, so you can only guess the possible reward.
Yes, when paying with fixed payments, bounty hunters can see in advance what amount in tokens or other cryptocurrency they will receive.
When paying with bets, this is not only not visible in advance, but also significantly increases the possibility of unfair manipulation of payments by the ICO team. This is very significant, because recently in almost all projects the team has not fulfilled the original obligations when paying bets. With a fixed payment, this usually does not happen. Therefore, for me, a fixed payment in this case is preferable.