If you have a MacBook running Mavericks, and it takes a long time to reconnect to WiFi upon waking from sleep (more than a few seconds, as long as a minute or two), you are not alone. This behavior has been reported hundreds of times on different discussion forums, and it seems to affect all models of MacBook, Macbook Pros, and Macbook Airs capable of running OS X 10.9.
A lot of fixes have surfaced that have helped some, including turning Airport off and back on, deleting the preferred WiFi network (in the Network system preference pane under Advanced) then reconnecting, reordering the preferred network order, and resetting the SMC. One fix that seems to have worked for everyone is disabling Bluetooth, so if you don’t use Bluetooth and are experiencing this problem, that would be my first recommendation. More info available at: https://discussions.apple.com/message/23561100