For infrantry Marines. Plus they are an all rounder unit. Good at both offense and defense. Very cost effective. 

Scouts. Often the most overlooked unit in the game. Extremely useful. Very cost efficient to enhance with Serum. And very useful for defence of your base, allied buildings and to send to defensive ops. 

Katana Light drones. Very cost effective defensive mech unit to build along with the kaiken Assault drone. Cost effective mech infrantry for offense. 

Armour and aircraft. For the rss it cost to build armour and aircraft. It is near triple the rss to get equivalent power then by building an amount of infrantry equivalent to the rss needed to build armour and aircraft. 

Basically what I said there is that it cost way more rss then it should to build armour and aircraft. So I recommend just spamming infrantry. 

Even ops is the same. Light and mech infrantry payouts are the best and more profitable in the game with less power loss then if you get armour and aircraft only rewards.

This is what the Russians do with their thousands of multi accounts. The same Russians that have made already near a dozen people I know quit the game today alone. 

Sparhawk

Thanks for your response.   It was informative on what you believe to be useful!  I agree that the armor, and aviation is costly!  Maybe it is a long term thing once we get our tech up and about..

Hopefully this response will encourage some other responses about their use of making units.