Stating the obvious, Horse Lord with Sandworm rules the land. Based on your preference, he is accompanied by Assasin, Barbarian, Valkyrie or Dread Knight. Elephant is a must at some point and the center is very important.
However I would like to point to coordination problem between the players in terms of production. I think the first turn is very critical for the team. Each team member must reveal their strategy to avoid redundancy. The way I see it, there are 3 ways to go.
1)Flyer, harrasers: Train Crows at the capital, capture the eagle city and keep sending flyers. At some point you may try Flying Barbarian for a surprise raid to enemies homeland or an Assasin Ghost Eagle Crow combo. Meanwhile slowly build your heroes and troops. Your homeland could be vulnerable for a while but you may end up razing a few cities or reducing the gold income from the enemy.
2)Scorpions:Train scorpions at the capital, plunder everything except the sandworm and keep training scorpions. You can't train too many stack bonus since you have to keep 5 scorpions in the stack for effectiveness. Scorpions have great mobility and you can get 6 scorpions together faster than your enemy getting a stack with Sandworm.
3)Rainbow: Use Heavy Infantry as defenders (or spiders later on) and train variety of troops. Occupy most of the cities. Make mix stacks using anything you can get a hold to like Sandworm-Battering Ram-Giant-Knights-Wolf Rider (Elephant-Unicorn if possible).
I think it is the best if each member of the team adopt one of the strategies above. otherwise you may end up with too many flyers, too few flyers or lack of serious hitting power or lack of mobility. For example if you start with Flyers and want to switch to scorpions, you will end up loosing money. So whoever trains flyers must teleport or send them to the other members, heavy infantries must be teleported to other team members hometowns so that the scorpions can start flowing and decide the game. Also sending gold to the team member to receive a high level heroes or heroes with Devil-Red Dragon ally can be game changing as well.
Thoughts?