The first thing that one should know about deadly snakes in the United States is that it is unlikely that you will ever encounter any of them. If you are a hiker, and find yourself in and around their habitat often, then you may occasionally come into contact with them. The truth is, the majority of these snakes are never seen by the average Joe. Still, that possibility exists and it makes sense to know about them.
Trying to figure out which is the deadliest snake is difficult. The reason for this is because you have to take into account a number of factors. For example, the coral snake is largely considered to have the most “deadly” venom, but they much more unusual to come across than say a cottonmouth. Also, the coral snake does not have the venom delivery system of the average rattlesnake. They have smaller fangs that are located in the rear of their mouth. While the coral snake can and does bite and deliver venom, it is much harder to do so than a rattlesnake with large fangs that can penetrate boots.
With this in mind, the two snakes that jump out at me are the Western Diamondback and the Eastern Diamondback rattlesnakes. The Mojave rattlesnake would likely be right there with these two if it were a bit more common, and more widespread. They are found in a pretty focused area that is often not inhabited by human beings. This leads to fewer bites, and therefore precludes their being included as one of the deadliest.
The Western Diamondback has no such qualms. They are around plenty of humans and do plenty of biting when compared to the majority of venomous snakes. Their venom is powerful, and they deliver the bite with large fangs that can give a large dose of that deadly venom. Many consider the Western Diamondback to be the deadliest snake in the United States.
For my money, the Eastern Diamondback is about as deadly as they come. This is not only the deadliest snake in America in my opinion, it is also the largest venomous snake as well. They grown big, fat, and can have a nasty disposition when they are bothered. The venom glands are huge on the eastern diamondback rattlesnake, and they are not shy about injecting that venom.
Of all the snakes in America, I call the Eastern Diamondback the deadliest overall. The Western diamondback is a close second, with the Mojave close behind them.