MOZART ALL THE WAY! :D
Beethoven: Composed German-style/language works
Mozart: Composed German AND Italian-style/language works
Beethoven: 1 opera, rarely performed
Mozart: Many still-successful operas, in Italian and German, with "The Marriage of Figaro" and "The Magic Flute" two of the most performed operas WORLDWIDE.
(Even if you're not an opera fan, I'd again argue diversity/success in multiple genres has to count.)
Beethoven excels in symphonies, with his 5th, 6th, and 9th especially famous, but Mozart has incredibly-popular and indelible symphonies as well, 29, 34, and 40, just to name three.
And Mozart began composing his first pieces when he was 8 years old or so...
MOZART 2014--NACHTMUSIK YOU CAN BELIEVE IN! ;)