I don't stream yet, but for the playback from HD I chose Airplay. WiFi makes all things on the computer side irrelevant. You can use any computer with any speed and any amount of RAM and it won't make a difference since what is being send is data in packets with no timing involved. Initially I had problem with dropouts, but it is OK since I switched to 5GHz band (more channels, less traffic).
The only thing that matters with WiFi is quality on the receiving end. My Airport Express outputs optical signal with small amount of jitter (280ps). According to what I've read jitter becomes audible above about 50ps. 280ps is not that bad, but fortunately I use DAC with strong jitter suppression.
From two other choices I would pick #2, because #1 can affect performance by injecting computer's electrical noise into DAC.
Other than injected noise async USB should be perfect being similar to WiFi (data transfer with no timing involved).