Possibly "Louie Louie," written by Richard Berry and originally performed by the Kingsmen. It's at least one of the most covered songs, if not the most covered. But most people think it's "Yesterday" by The Beatles.
Yesterday
No one really knows what that is but it might be Welcome to the Jungle by Guns n' Roses because it listed number 1 on VH1's top 100 rock songs. Or not. The most famous rock song ever is still Rock Around the Clock by Bill Haley and His Comets, which was also the first Rock #1 ever.
Yesterday is the most covered song in the world, so that could be a contender. There's so many that are instantly recognisable.
Rock Around the Clock, by Bill Haley and His Comets.
No one has covered "Layla" other than "Pickin On" and that doesn't count. Layla is unique and no one has the skills of Eric Clapton and late Duane Allman to pull it off. Best Rock Song Ever.
probably Stairway To Heaven by Led Zeppelin or Bohemian Rhapsody by Queen
Its all in your opinion.
bad romance
The lemonheads is the famous 90s alt rock version
Hardcore
No
It's all in your opinion.