If you compare all the accomplishments between the two, no contest. There is a reason he was called the Cannibal.
Just to start, here is a wikipedia quote: "
widely seen as the most successful rider in the history of competitive cycling. His victories include an unequalled eleven Grand Tours (five Tours of France, five Tours of Italy, and a Tour of Spain), all five Monuments, three World Championships, the hour record, every major one-day race other than Paris–Tours, and extensive victories on the track."
"As a road cyclist, Cavendish turned professional in 2005, and achieved eleven wins in his first professional season. Cavendish has won 33 Tour de France stages, putting him second on the all-time list, contributing to a third-highest total of fifty Grand Tour stage victories. He won the Men's road race at the 2011 road world championships, becoming the second male British rider to do so after Tom Simpson. Cavendish also won the points classification in all three of the grand tours: the 2010 Vuelta a España, the 2011 Tour de France, and the 2013 Giro d'Italia. In 2012, he became the first person to win the final Champs-Élysées stage in the Tour de France in four consecutive years."