The only time Ive ever had issues with OS X connecting to wifi was while using a cheapo router that insisted on advertising its 2.4GHz and 5GHz networks using the same SSID.
Moving to a router that allowed them to be configured with different SSIDs resolved all my issues.
> The only time Ive ever had issues with OS X connecting to wifi was while using a cheapo router that insisted on advertising its 2.4GHz and 5GHz networks using the same SSID.
That is the default behaviour for an Airport Extreme.
Moving to a router that allowed them to be configured with different SSIDs resolved all my issues.