I fly this route about every 1 to 2 months, and travel on BR most of the time between Taiwan and China.
I've been on all classes, J,M(Premium Economy[Called Elite Class]),Y.

For J the seats are angle lie-flat. Food and Wine service is really nice, well-presented and taste great. You can select meals online if traveling on BR ticket. The FA are also very friendly like most of the asian airlines, but sometimes their English skills are limited(what I heard from other FTers in Asian forum, I speak Mandarin & Taiwanese anyways).

AC doesn't sell PE tickets, but this is the cabin I travel most of the time, much more comfy than Y. About 1.25~2x more expensive than Y. Sometimes you can get deeply discounted PE fare which is only about 10% more expensive than Y with a Taiwanese/Chinese travel agency.

Y seats are slightly narrower than AC's. The entertainment system pretty good, AVOD, 8.4 inches, touch screen. B744 and B77W are flying this route, if you get B744 and are flying Y, ask for upper deck seats because the seat-pitch 36 inches compare to main-deck 33 inches. Food is fine, slightly better than AC Y meals.

No AC UG cert, but I heard people buy up at check-in which sometimes can be a good deal.

Not sure about *A priority, because I'm BR Gold at the same time.

BR is often dicussed in the Asian forum, search it up.
A BR C Text Trip Report written by ak333