I have to agree with the OP that the American program has a considerable Advantage over Mileage Plus.
I am a former 1k/Premeir Executive for many years prior to climbing on board
My reasons for defecting to AA include

• Superior Award Availability (#1 reason)
• No pressure to earn elite status already Lifetime Platinum
I am currently cruising my way to the 3 million mile mark
• Access to British Airways Int First and Business Class seats (non Trans Atlantic)
• Non expiring electronic upgrades for those who remain elite
• Nicer Club Rooms/ Free Computer usage
• No Outsourced/Overseas call centers
• More competitive pricing on tickets
• Excellent Program more exceptional ways to earn miles
Less hassles understanding the majority of their simple less conditional promos
• Vastly improved pro active account customer service posting partner miles within 24 to 48 hours that was not their responsibility
• Superior response when the need for consumer relations arises
Sadly United ruled in years past in this area.
• No worries when booking award tickets for friends and family members that I have to go the airport and sign before they travel.
American for the most part makes doing business a pleasure
• And yes flexibility with award stopovers rock as does the 17,500 mileage round trip awards to select markets through the citibank AA matercard partnership

The biggest negative on average with AA is in flight staff crews IMO
Not to happy or friendly
United's flight attendants were in the years I flew them on as good as it gets within the Domestic US.
That said AA does have some fair performers on board too.
The friendly more interesting UA folks are missed along with the 767s I preferred on the Transcons.
I flew PS in first once didn’t like it and never booked again. I would like to try business class one day as it looks more comfortable....