There is no difference between the mIRC versions on the download page. The locations simply specify where the mIRC.exe is being hosted. It's best to choose a connection closest to you to ensure a quick and easy download. That's all.
It doesn't matter hugely which server you connect to on a network. You might get less lag on a server hosted closer to your location, but usually this is negligible (in my experience anyway).
Nevertheless, should you wish to force mIRC to connect to the German server when it starts up, you could use:
ON *:START:{ server german.server.here }
(Put this in Remotes, ALT+R > File > New).
Regards,