Count me in with those who can't really think of a Beatles cover that I prefer over the original, though I'm definitely not of the camp that believes they should never be covered.
In fact, two of my favorite bands, The Dave Matthews Band and Toad the Wet Sprocket (now defunct), have both covered Hey Bulldog quite well! In live settings, I love their renditions (nothing like the raw energy of live sound to really give "umph" to that song), but it's a different creature from what The Beatles put on tape, and I can't say I find it superior.
Somewhat hypocritically though, I do find some covers done by The Beatles to be superior to the original (Twist and Shout comes immediately to mind).
Damn it, just replying to this thread reminds me how much we need either remastered CDs, or hi-res versions (or both!) of The Beatles catalog!

Talk about something that would drive a hi-res music format (since porn's not an option)
