It is the TO's call but of course input from the group tends to make happier players... When there is a big tournament coming up we have folks bring their customizable maps and we just run that for about a month before the tournament (Nats, Worls, Realms, etc...)
Otherwise, since we have a lot of maps from various BG kits I send out a note letting them know which map we are using. If there is a specific request that can usually be accommodated. But otherwise... just pick! The deluxe rulebook has some maps toward the back you can use your customizable ones for as well..
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Austin, TX Info for Worlds!