No they don't compare. Why? Because they're different tier levels.
The Special Forces community in the US Military is a lot bigger than you think. The lowest tier over a conventional unit such as the 82nd Airborne Division or 1st Marine Division would be the 75th Ranger Regiment, Marine Force Recon, etc.
Next would be actual Army Special Force, which are all the 18 series MOS's.
After that, you would have CAG, which is 1st SFOD-D or more commonly known as Delta Force. Delta Force is America's elite counter-terrorist force and they are modeled after the SAS from their mission set to their unit organization. CAG is one of the elite counter-terrorism units (along with everything else they do) in the world, and are right on par with the SAS. Is either one of them better? Nobody could tell you that because nobody here is either one of them, and if they were, they wouldn't know much about the other unit. I've had the chance to work with each of them on a few missions in Iraq, and they are top notch.
But comparing SAS to Special Forces is along the lines of comparing apples to oranges. But comparing them to other top tier units such as CAG ... they're all really freakin' good and you can't get much of a better answer than that.