I think just one new unit would be a good idea, as these changes have made things a lot tougher to play both games, attacking and defending. Its very hard for an attacker to get hold of a planet with the weak defence of the droid, but the soldier really isn't an option for an attacker. I do like the soldier improved to match the attack of a droid when defending, means bankers might be able to defend themselves for a change!
I think there should be three units, set up as follows...
Unit 1
Attack 2
Defence 8
Unit 2
Attack 5
Defence 6
Unit 3
Attack 8
Defence 2
Values ofc can be fiddled, but thats the idea. Essentially the attacker has a choice, either use the third unit and wreck havok once you get going, or the second which is easier to get into systems but then you need more to take a planet. Building a mix isn't really an option.
enjoy them! 
