In MEL the SQ lounge wins HANDS DOWN. it is open early before the 11:15am flight, but only about an hour or 2 when the flight departs at 3:15. The Koru lounge is second choice, nut with very nice wines. The UA lounge is a dump, and an overly crowded one at that.
Only problem is you won't hear when they cancel your flight in the other lounges (and chances are they will, the track record hasn't been very good lately)

btw last month they let us right into the SQ lounge with our BPs, but last week the agent insisted in seeing our actual cards. (at least one of them)