The Wing is a bit bigger and more busy usually, since it is right after security and close to the duty free. Whereas Pier is closer to the gates and a bit more subdued, which can be a good thing as during peak times seats are hard to find at the J section of Wing (a bit better in F).
Ive also heard of people using Wing upon arrival to HKG
for showers, etc. I have not done so, but its a good option if coming in long-haul.