I have both UA and AS points. I want both of them and I use both of them. UA points are tremendously valuable for European business class travel for two. I book 11 months out. I find excellent availability on the nonstop Austrian flight from LAX-VIE with connecting service onward. AS only has BA with its heavy fuel surcharges as an option. I recently used AS miles to fly JNB-HKG-LAX on CX in a combination of biz and F. It was an incredible value. I have an upcoming trip where I'll fly Fiji Airways to Fiji and on to Sydney.
AS has a mini hub in San Diego. Redemptions can be excellent value in coach on nonstop flights.
If I didn't live in an AS hub or able to easily drive to LAX to access their partners, I wouldn't find AS very interesting.