Hi E.Canon2014 and welcome to posting. I have frequently sought advice from this forum and have had some terrific help before!
Regarding your dilemma, well I have been on a BA A380, once in J on the top deck, and recently on Y+/Premium Econom (from IAD to LHR), and I would be very happy to try the premium economy again, even on a much longer flight.. The seat is actually very comfortable and gives reasonable space. The entertainment system has loads on it and it is easy to use.
You would also get more BA Avios..
I am sure the Cathay product is decent, especially with the soft product, but remember the first meal you will get a business class standard main course.
I hope this helps.