How should I place my skill points?

[Ronzer]

I'm playing as the UK and I'm level 13. So far, I've put my skill points only into defence and energy on a ratio of 1:2. But is energy really important? Is doing missions even important? Or is it best to put points into attack, defence and stamina on a ratio of 1:1:1? Also, what units should I purchase to give me the best advantage in fights against rivals?
I'm sorry if this has been asked before. I used the search bar, but I couldn't find anything related to my question.

[Agent Orange]

Depnds on how you play, my llp is all out attack. Everything into stamina and attack and playing under Russian flag with heavy super hornet army.

[Ronzer]

What if you were to get attacked though? What chances do you have if you are all out attack? Now you're making me wonder whether or not defence is important.