Ping both servers and see who is the quickest.
And if you are using linux, you may try mtr for the link quality.
Syntax => mtr --report -w solo.ckpool.org for the us server and
Syntax => mtr --report -w de.ckpool.org for the german server
cheers - wasn't sure if it was that simple!
big difference in pings though
de.ckpool.org - 34
solo.ckpool.org - 148