WiFi problems on Mavericks
I had very unstable WiFi when I upgraded my late-2012 Retina MacBook Pro to Mavericks (model: MacBookPro10,1). Upon waking from sleep, my MacBook usually wouldn't connect to WiFi. I had to try manually reconnecting several times to get a connection.
The solution for me turned out to be trashing my Bluetooth preferences file (
/Library/Preferences/com.apple.Bluetooth.plist) and restarting.
Instructions courtesy of Peter Cohen!