For the arena we have to distinguish two cases
- 1. During Arena Challenges
- During Arena Challenge one looses points if the defense is defeated. So this has to be avoided by a good and versatile defense. There's no ideal defense as this depends on the own units, their ranks and the player level.
- 2. No Arena Challenge ongoing
- You win a small amount of gold if your defense wins. And you loose nothing if your defense looses. Nobody will attack you if you have a strong defense - nothing to win for you and the others. But you can profit from the arena by attacking defenses with drop formations:
- 2 Wimp (r6) in second or third row
- 2 Lightning Dragoon on the side
- Light Chemical Tank on the side
- Chucker in first row
- Sandbags or Portable Walls if you don't have light chem tanks or lightning dragoon
- trooper in third row if no wimps are available or on low rank
I use drop formations myself for my farming accounts and outside of arena challenges on my main account.
Winning a arena fight gives an additional xp and gold reward. The gold reward is about 30k at level 40 and about 55k on level 70.