Ladies and gentlemen, it's the main event of 19th-century opera! In this corner, sporting facial hair resembling a terrier, composer of 26 operas, the man from Milan, the Italian Stallion, Giuuuuuuseppe Veeeeerdiiiiiii. Over here, rockin' the neck beard, the composer of 13 operas, the bad boy from Bayreuth, the Teutonic Terror, Richard Wagnerrrrrrrr.
Who was the greater innovator?
Before Wagner, operas were like musicals with no spoken dialogue; a series of extended songs with sung material in between to move the plot along. Wagner changed that by writing operas where the music continuously evolves, in the process devising harmonies and orchestral sounds no one had heard before. Wagner pioneered the use of leitmotivs. With some tweaking, the tradition of introduction-song-repeat-until-hero-or-heroine-dies suited Verdi.
Who was the superior tunesmith?
It's not hard to guess who wrote the melodies that people went home humming.
Who's more popular currently?
Verdi had great success in the middle of the 19th century, but by the time he died in 1901 Pagliacci and Puccini were setting the trends in Italian opera. Wagner was his own best promoter, writing dozens of articles and books convincing folks that he was the future of opera. Critics agreed, and so did opera house managers -- by 1901, Wagner was considered the greatest opera composer of the 19th century.
These days the situation has reversed. For every single performance of a Wagner opera, there are ten of La Traviata or Aida. Audiences love a good tune, and they don't have to sit around for five hours to get through a Verdi opera.