They're quite similar Civs... the pros and cons:
Iroquois:
Pro:
Mounted Warrior - 3 attack, fast, 30 shields, upgrade to knight
Commercial - Gold can offset growth unhappiness, gold is more versatile
Only need horses; No horses, may still build nice army with iron
Con:
Commercial - Effect doesn't show fast
Mounted Warrior - 1 defense (is this a real problem?)
Celts:
Pro:
Religious - short anarchy, cheap temples, temples can offset growth unhappiness
Gallic Swordsman - 3 attack, 2 defense, fast
Con:
Gallic Swordsman - 40 shields
Need iron; Can't build nice army without it really.
It takes longer to mobilize a good military with Brennus, but does the religious trait make up or that?
Hiawatha can upgrade his mounted warriors to knights though (and then to cavalry)... a great advantage I think.
I'm leaning toward Hiawatha.
Whoops, forgot to make it a poll. Oh well, then maybe people won't vote without explaining why.
Iroquois:
Pro:
Mounted Warrior - 3 attack, fast, 30 shields, upgrade to knight
Commercial - Gold can offset growth unhappiness, gold is more versatile
Only need horses; No horses, may still build nice army with iron
Con:
Commercial - Effect doesn't show fast
Mounted Warrior - 1 defense (is this a real problem?)
Celts:
Pro:
Religious - short anarchy, cheap temples, temples can offset growth unhappiness
Gallic Swordsman - 3 attack, 2 defense, fast
Con:
Gallic Swordsman - 40 shields

Need iron; Can't build nice army without it really.
It takes longer to mobilize a good military with Brennus, but does the religious trait make up or that?
Hiawatha can upgrade his mounted warriors to knights though (and then to cavalry)... a great advantage I think.
I'm leaning toward Hiawatha.
Whoops, forgot to make it a poll. Oh well, then maybe people won't vote without explaining why.