I am often asked this question, which, I have to say, is rather silly.

The short answer is that I much prefer {London AND Paris} to {London} OR {Paris}.

These are two very different cities, with very different lifestyles and infrastructures, each is better than the other for certain types of activity.
A regular change of scene (and language) is very refreshing, it re-sets the mind, it refocuses the eye.