I know how frustrating this is as I have been wrestling with wifi issues for months. It came to a head the last couple of days and I've solved it. I'm on a Retina Macbook Pro 13" (Ivy Bridge) Mavericks 10.9.5 connecting to a Sonicwall TZ100. This wireless AP is a 2.4GHz model only but does support 802.11n. The symptoms were frequent disconnections where you had to go to the network icon and reconnect to the wireless AP.
I used MacOS Wireless Diagnostics to capture the problem and MacOS Console to review the logs. I was getting frequent Airport errors logged as "AirPort: Link Down on en0.", these were mostly "Reason 2 (Previous authentication no longer valid)" but rarely also "Reason 8 (Disassociated because station leaving)".
I tried all sorts of solutions from the various internet forums but what has solved my issues was to change the router from WPA/WPA2 security to WEP. This is not an ideal solution for two reasons: (a) WEP is very insecure; (b) 802.11n only achieves full performance via WPA2 connections. However I'm very pleased to no longer have any dropouts. I can confirm this because I was able to reproduce the dropouts easily by uploading a large file to an FTP site. Now I can upload lots of large files to an FTP site all day with not one problem.
My suspicion of the root cause is an incompatibility between the Broadcom BCM43xx firmware/driver and the wireless AP chipset firmware/driver (Atheros 9100?). It is possible that using a 5GHz connection would solve the issue but that frequency is unsupported by the wireless AP. In addition I have no way of updating the wireless AP firmware so I am now considering purchasing a new wireless AP, I think that is the best solution for this issue.