Which stings from wasps, hornets or yellow jackets are the most dangerous?

Depends: They are about the same unless you are severely allergic to one and not the others.

All are potentially : There is no distinction between these groups of stinging insects as to which one is worse. Typically yellow jackets are the more aggressive species and the one more likely to sting an individual but all can be dangerous.

Hornets: Hornets ; yellow jackets are both wasps. Hornet stings are usually more painful than other wasps because their venom contains 5% acetylcholine. Some hornet species have extremely toxic venom. The asian giant hornet has the most dangerous venom ; is responsible for many deaths every year. Single stings are not usually lethal (severe allergies can be the exception to this rule). Both yellow jackets.