Ostheer Pools

For Ostheer, which pool should I pick from the beginning against all the Allied factions in 1 v 1? Which situations call for changing unit pools? I would like to know specifically for all the Allied factions, but mostly Americans and Soviets.

In 2.300 you should start with support and make support mortar.

Assault mortar works like artillery - you have to order it to fire a barrage everytime but cooldown is low and it has a high range.
Support mortar fires automatically and has a lower range but you are not screwed when your enemies moves to different position.

Agressive has overall stronger units

I like getting the HMG34 Team.

Defensive, HMG34 / Kübelwagen tactic works pretty well, too. Push enemy with the kübel while the mg34 sets up in the background