Can an American join the SAS?

"Also, is the SAS really the deadliest most well equipped and best trained special forces unit in the world? Or does that title belong to an American Special Forces unit like Delta Force or SEAL Team 6? "

There is NO appreciable difference between the various top SOF units in the world. They are all equipped, trained, and experienced in roughly the same degree, except insofar as some are designed to perform different missions (for instance, one unit might not train to use small boats).

You take any of the major top tier SOF units and they will be just about as effective at most of their missions - in fact, many of them train with each other (at least within the NATO alliance). Some are better in certain environments or at certain missions, some have more backup, but they're all trained and equipped just about as well.

If I were a terrorist group holding hostages, I'd be equally terrified of the notion of being attacked by SAS, DEVGRU, French Naval Commandos, whatever the top Russian Spetznaz group is, etc. They can all kill me and my group just about as well.

You could also apply some common sense:

With a few exception (like the FFL), you can only join the army of a country if you have the citizenship of that country.

Regarding the 2nd part of your question: There is NO such title.. well except for wannabee kids on this forum. All Special Forces within NATO are trained at the highest standards .. and if they've been ordered to find and kill you, they will kill you .. Period !

Whoever told you that is wrong.

The British SASR have the same rules as every other Regiment in the British Military in that you must be a British, Irish or Commonwealth citizen and must meet the residential criteria to be eligible to apply.

The only way you could do it would be gain British citizenship, join the British military for around 3 years and then apply for selection.

The US Ranger Regiment also use completely different stick formations, rigs, canopies and jump equipment to us and as such also use and train using a different static line technique to our British Airborne

Nope. Joining the SAS would require that you be a British subject and a veteran of British military service. While SEALS, Army SF and others are occasionally posted to one of the SAS units, they are put there as observers and liaison assets, not as members of the unit.

Forget what you heard.

Unless you are a member of the British Military YOU wont be joining the S.A.S. period.