There is no obvious answer, people prefer different ways, some like by donations some like by power or attendance and etc. Pick one that you feel best represents your group and * with it, people who won't like it might go but people who stay are probably staying for good and you might get new people from other groups who find your system more appealing.

We also do it by spreadsheet like the guy above, but only by gnw attendance, show up to fight 5 times and you get 5 times more seal scrolls then guy who only shows up once in the long run. Imo it's the most fair and it encourages weaker/newer people to show up for wars. Sure some bigger p2w players won't like this system since they might feel they are contributing more then weaker players but that's the direction we chose to go.

I would rather be 4-8 because that means there is at least 4-8 groups doing gnw lol.