People get upset when they feel something isn't fair.
Yet fairness isn't about the outcome, it's about the process.
You won't make people any happier by changing the outcome. You will make them happier by engaging them to develop a better process.
If they don't like the outcome, ask where the process failed. Correct that stage in the process.
The best approach is often to let members create the process for themselves to abide by. Your job is then to follow that process. Don't tweak outcomes, tweak processes.