The food, drinks and service are pretty much identical in both lounges. The main differences in my mind:

Location: I'm usually travelling to/from North America, so my flights usually depart from the gates closer to the Wing.

Space: The Wing is built on an open platform on top of the main concourse level of HKG. The ceiling is the roof of the terminal, giving the lounge an airy feel. The Pier is not claustrophobic, but it definitely feels cozier, what with the lower lighting and the darker environs.

Internet Access: The Pier has more computer terminals, if that's important to you. Both lounges have WiFi.

That's my $.02.