The Mid Wests, a one day contest, have always been world cup style; round robin group records seeding a single elimination bracket. We feel that this guarantees the most games for participants, and if the groups are done well, the best competition.
I hear the NACCCs, a two day contest, are going to be round robin groups on Saturday seeding a double elimination bracket on Sunday. So all comers are assured multiple games on both days.
I'm loving the announced and set-aside time for friendlies before/during/and after these big tournaments.
What else is being/has been tried? Success? What criteria are you using to form your groups or brackets?