I've got a fair few cover versions and they vary between 'better than the original' and 'I think I need to go and listen to the original now. Actually, please give me some brain bleach first.'
But I tend to find them interesting regardless.
Then there's the cheekier things like Billy Bragg's 'Ideology' which really is just 'Chimes of Freedom' with different words.
But yes...
There will only ever be one version of Comfortably Numb - the one by Pink Floyd.
There will only ever be one version of Will You Still Love Me Tomorrow - the one by Carole King.
There will only ever be one version of With a Little Help From My Friends - the one by The Beatles.
As to preferring the first version you hear, well, I heard Metallica's version of Stone Cold Crazy first, and I prefer the original...
As an aside. Of songs that have the same title, but aren't the same song...
Evil Woman - Black Sabbath, ELO, or Spooky Tooth?
Heaven Can Wait - Meat Loaf or Iron Maiden?