When I was in charge of a group we had pretty easy pack distribution. I had an excel sheet with every player participating in gnw. I had their activity and donation numbers, I was updating them after every week and we had a simple rule, packs were given only to players with 100% gnw participation, first of all players with the highest activity and donation. After they've got their packs they were out of the list for 2-3 weeks depends on how many active players we had. I think its the most fair way to distribute packs.

Sorry for bad english, its not my native language but im trying my best :sss