Regarding China Airlines, they don't have a good safety record, but their inflight service is fine.

My friend who took China Airlines says their pitch is not bad, and considering you are flying HKG-BKK which is a relatively short flight, you can just pick window or aisle based on your own preference. However, for the 2-4-2 seats at the back, some people like it if you are travelling in a party of two. However, I always found the back of the plane tends to be shakier and since there are washrooms at the back of the plane, many people will hang around (or queue for washrooms) that area.