Unlike Delta Force, Navy SEALs are officially acknowledged by the U.S. government, as well as everyone else; it's hard to ignore their existence when they've been credited - very publicly - as the team behind the killing of terrorist mastermind Osama bin Laden. Sadly, members of the elite Navy SEAL Team 6 were killed when Afghan insurgents shot down a Chinook transport helicopter in August of this year - but that should not take away from their "tough" factor in this article of comparison; it should be of note that Delta Force has also had their bad days too, most notably their failed attempt at rescuing 66 American hostages in Iran in 1980, which coincidentally resulted in a fatal helicopter crash.
But I digress. Navy SEALs, like Delta Force, are super soldiers specially trained for unconventional warfare, reconnaissance, and counter-terrorism operations on SEa, Air and Land (hence their acronym moniker). Created by President Kennedy in 1962, the Navy SEALs emerged from the elite of the U.S. Navy to parallel the Army's Green Berets, when tasked to infiltrate and disable enemy jungle camps during the Vietnam War. Since then, the Navy SEALs have evolved into a formidable and revered unit on their own, and is now a part of U.S. Special Operations Forces.
According to The New York Times, Navy SEALs must train for at least six months before deployment, including dealing with free fall and underwater scenarios, demolition training, and engaging in hostage and terrorist simulations. They must also go through a grueling test of endurance; during "Hell week" trainees must run, swim in cold water, and crawl through mud almost non-stop for almost six days, with only a total of four hours sleep. Only about half of the candidates survive training, thus filtering out the incapable.
Navy SEALs are organized into Teams 1 to 5 and 7 to 10, some of them with a specialty beyond their already intelligent and deadly skill set. (SEAL Team 2 specializes in arctic combat, for example.) But if we are trying to compare the toughest with the toughest, we have to talk about SEAL Team 6, the "all-star team" of SEALs formed as an alternate elite unit after Delta Force failed at rescuing the hostages in Iran. Team 6 is so superior to the already stellar SEALs that they've branched out and became DEVGRU, the U.S. Naval Special Warfare DEVelopment GRoUp. They require even more training after their time being "regular" SEALs, including scenarios like parachuting from 30,000 feet in order to gain control of a hijacked cruise liner.
And The Winner Is...
Based on what I've reported here, one might think that Navy SEALs - particularly Team 6/DEVGRU - would be the tougher of the two when comparing them to Delta Force; they have more intense training (that we know about), and were even created in response to one of Delta Force's botched missions. However, to say the Navy SEALs are tougher than Delta Force is an unfair argument because you have to consider just what exactly makes a soldier tougher?
Quantitatively, you can say the amount of training, but in the real world it really boils down to the particular mission at hand. And every mission is different, with its own unique obstacles, element of danger, and military strategy. Both the Navy SEALs and Delta Force are SMUs (Special Mission Units) under U.S. Special Operation Forces and sometimes work together (unofficially, of course). Could Delta Force have taken out Osama bin Laden if they had been tasked with the job? I think that they might have had the ability to do so - however, they just didn't get that assignment, so we'll never know.
In the end, there's no real definitive answer to who is tougher between Navy SEALs and Delta Force - they're both badasses in my opinion - and if you favor either one over the other in terms of being tougher, that's pretty much like taking sides in an evenly matched Army vs. Navy football game. Besides, I dare not side with either unit in this comparison of toughness; I know both have the capacity to find me and take me out.