Within the borders of Europe, there are more German speakers than French speakers.

Worldwide, there are actually more French speakers. This is because there are many parts of the world - particularly in Africa - where French is spoken as a second language and as a medium of communication in education and trade. French will serve you well in around 26 countries of Africa, plus parts of Canada, the Caribbean and the Pacific. German is confined to Europe.

But even if you only want to travel in Europe, French is still a more useful language than German. This is because, in general, German speakers are much better at speaking English than French speakers are. Wherever you go in German-speaking areas, you are almost certain to find people who speak English well. You may find it difficult to spend time in France if you don't speak French, though.

I recently read an article that stated that there are 76 million native French speakers and 78 million native German speakers.  If you add places where French is spoken as a second language (large parts of Africa and the Caribbean) the number increases to 220 million.  A quick Google search says that total number of German speakers (native plus as a second language) is 229 million.  So looks like they are EQUALLY used... pretty surprising as I would have thought French would be used much more!  But these are Google facts... so maybe not the most accurate.