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We already played as the Barbarian and Warlock in HoMM3 2007.
I suggest Knight and Wizard for stages 2-7, respectively.
HoMM3 2007 statistics:
Stage 1: Knight
Stage 2: Barbarian
Stage 3: Rampart (Elves)
Stage 4: Chaos
Stage 5: Necromancer
Stage 6: Sorceress
Stage 7: Warlock
Stage 8: Swamp
Stage 9: Life
Stage 10: Mage (Academy)
Added a couple of minutes later
I suggest a starting castle option for HoMM3 2008: Stage 1: Barbarian (already chosen) Stage 2: Knight Stage 3: Barbarian (Inferno Castle) Stage 4: Death (Nature) Stage 5: Dark Elves (Inferno) Stage 6: Warlock (definitely, as all others have already been used) Stage 7: Wizard (possibly Sorceress) Stage 8: Tower (Dungeon) Stage 9: Order Stage 10: Orda (Fortress) P.S. But in general, the organizer will know best which castle to choose depending on the specifics of the map for the tournament.
Added a couple of minutes later
I suggest a starting castle option for HoMM3 2008: Stage 1: Barbarian (already chosen) Stage 2: Knight Stage 3: Barbarian (Inferno Castle) Stage 4: Death (Nature) Stage 5: Dark Elves (Inferno) Stage 6: Warlock (definitely, as all others have already been used) Stage 7: Wizard (possibly Sorceress) Stage 8: Tower (Dungeon) Stage 9: Order Stage 10: Orda (Fortress) P.S. But in general, the organizer will know best which castle to choose depending on the specifics of the map for the tournament.