Guess it really comes down to what you spend for your tickets. Isn't Platinum 9 miles per dollar? At AA, the Gold level brings in 100% miles plus 25% bonus miles. I don't know where you fall in mileage accumulation to tell where you do better. If a leisure flyer like me, you might bring in more miles at the 25K/Gold level at AA.

Don't UA Platinum's get free redeposit of award tickets? You only see that at the EXP level at AA. If you do a lot of award travel. that benefit alone could make the decision for you.

Too many factors in play to really point you one way or the other.