There is no bestest setting cause it depends on conditions, usually network conditions, (a connection to a server is a network connection).
If connection to your service works great and you have very good network, adjust it to a lower number 0-1-2
If you have high latency, high ping, vpn or not so good ISP and network, adjust it to a higher number >10
Buffer Time can effect two things. When you are zapping channels and when a channel buffers while viewing the channel.
When a channel 'buffers' and with a higher buffer time set, then the longer it would take for the channel to reappear. The lower the setting, then it'd be quicker for the channel will appear. The longer buffer time is to allow more stream to preload before playback, so it would not freeze as much because it's got more preloaded, kinda thing. In theory. But Not all freezing is 'network' buffering though, so the buffer time setting may not have an effect.