FarangDemon's Strategy Quiz #1

I am conducting a series of strategy quizzes. Player(s) who posts the best answer or answers, according to my judgment, during the next 24 hours will be deemed "winner". If you want to win, you'll need a good explanation / explain the results of your calculations. I'll keep track of "winners" over time.
Note: if your answer is correct but your explanation incomplete, someone else may come along, building off your answer with a more complete explanation. They will be deemed winner, not you.
1. You are playing a no spoils, quads game, and so far, everybody is still alive. You have a weak opponent but your teammate is even weaker. On your turn you can choose to:
What do you do and why?
Remember, if you want to win, you'll need a good explanation / explain the results of your calculations.
Note: if your answer is correct but your explanation incomplete, someone else may come along, building off your answer with a more complete explanation. They will be deemed winner, not you.
1. You are playing a no spoils, quads game, and so far, everybody is still alive. You have a weak opponent but your teammate is even weaker. On your turn you can choose to:
- Attempt to defeat the weaker opponent with 64% chance, but then your partner will die at 80% on subsequent turn
- Attempt to defend your partner, your opponent will live at 100% chance, but your partner will die at 40% chance next turn
What do you do and why?
Remember, if you want to win, you'll need a good explanation / explain the results of your calculations.