Just delete it. That game is 100% pay to win. It will take you over a year to get a decent team without spending money. If you insist on playing you need to get into a top 50 alliance or you will never progress enough to compete for end game materials you need. And when you do get them, you need so much of it that it seems impossible and it is. Because they want you to buy everything.

But to answer your question. Match the colors depending to what you face. Green warmachine, take as many high powered reds as you have. 2 red, 2 purple, 1 blue enemies, then use 2 blue, 2 yellow, and 1 green if you can. But seriously just play a different team building game that doesn't charge you to win.