I have been to Oase and World in Frankfurt & also Artemis in Berlin.  I tell you I have more mind (and other) blowing experiences at Artemis than the others.  However, it also depends on what you are looking for.  I think Artemis has more German girls than other places.  At World on average girls to me seem less attractive, but there is always 1 or 2 drop dead stunners that you can have a session without a problem - that might be because many guys don't go there looking for a hottie.  Oase just has many pretty girls.  That's my 2 cents.