Do you choose to go first or second before or after revealing battlefields?

Ruling: You choose turn order after battlefields are selected. Battlefields are always face-up when selected according to the rules.

Sequence:

• Players select battlefields (face-up)
• Turn order is chosen

Nuances:

• Players commonly place battlefields face-down temporarily to prevent information leakage before both are selected, but this is not a rules requirement
• Battlefields could equally be held in hand and revealed simultaneously
• In games 2 and 3 of a best-of-three match, players know who will choose turn order and can make assumptions accordingly