Someone said the Shaggs, someone said Ellington. Let me be the first to say the Shaggs and Ellington.
There will never be a consensus on the "best." OP should have asked what our favorite American band is. Mine - The original James Gang.
If we're discussing genres other than rock n roll, it's Bill Monroe & the Bluegrass Boys (a finishing school that makes John Mayall's Bluesbreakers come across as kindergarten in comparison)
This has been done 100 times before. Maybe the threads can be combined? Anyways, the correct answers are: KISS or the Ramones