Twins. It does more damage than firebird, freeze, hammer, vulcan, etc at close range and it has infinite ammo unlike the others.

I remember the time when the Double Power powerup existed. I think there should be an actual double power (pushing power of your tank) or maybe triple power so you can push other tanks around.

Maybe a mode where planes drop bombs that deal area damage to tanks once in a while

The double damage powerup gives a 100% increase in damage. The double armor powerup gives a 100% increase in "armor". But the speed boost is just 30%. It's not as powerful as the other ones. A 100% boost in speed might be more balanced.