I've just finished flying AA's PE product between MIA and GIG on a B772.
While I can't compare AA's PE to that of UA or DL, I can agree with others that the seat is very comfortable and legroom (non-bulkhead) quite good. Also, with respect to personal space, there is enough separation between pairs so that is not an issue. Not noted in previous comments is the small State Street amenity kit, which is quite respectable and with the canvas case, quite repurposeable. The toothbrush is functional and hand lotion and lip balm are adequate for such a kit. (Socks and eyeshade also provided.) A 500-ml bottle of water is also supplied along with the pillow snd blanket package.
The two criticisms I have are about aspects of both the soft and hard products. While the main meal is a cut above coach, it is somewhat below business. But what really irked me was the use of plastic cups vs real glass wear for drinks and meal beverages. And a pre-flight offering of even water and juice (if not sparkling wine) would be an appropriate enhancement. As for the hard product, at least on the B772, there are no dedicated nor adjacent washrooms for this cabin. The closest washrooms are in the mid-section of the coach cabins and thus require a walk along a very narrow aisle. And when the cabin is darkened snd people are sleeping, this involves not tripping over blankets or hitting elbows and sometimes heads leaning into the aisle! (Some people did enter the business cabin to use the washrooms between the first and second J cabins and it didn't appear they were chastised by crew for doing so.)
As for the relative value between MCE and PE, that's another question since it comes down to the actual price and one's status. I've also flown MCE (to Europe on an A330) as well as to/from South America on the B773. In both cases I found the extra leg room made the flight a bit more bearable and as on all occasions I had an aisle seat with an empty seat next to me, I felt both personal space snd overall comfort was acceptable. The seat didn't cost me additional $s as I was an elite. Paying $150+ might be a different consideration depending upon what your original fare was. But there is a difference from one aircraft type to another. On the B773, the placement of MCE seats (aside from bulkheads and emergency exit rows, which I personally don't like because of the fixed seat divider snd the way the video screen and tray function) is awkward and don't correspond between window and centre banks. As well, I found most crews are unaware of these seats and thus have to be reminded you're in an MCE seat and are entitled to free hard alcoholic drinks on routes where there is a charge. And I found the A330 much better as MCE is s separate cabin (as it used to be on the B773s before PE) and has adjacent washrooms.
My PE fare was a ridiculously low U$600 rtn between YYZ-MIA-YYZ (in Y) MIA-GIG-MIA (in PE) so a no-brainer. Were it the more usual U$1200, I might have opted to MCE.