With a spray that reaches 27 feet, the safest spray to use for the user is Spectracide Wasp & Hornet Killer. This type of distance lets you reach some of the highest built nests around your property, or if they are lower, the distance allows a safe and secure buffer between you and any angry wasps. It is made of Lambda-cyhalothrin, which is a synthetic pyrethrin, made from the chrysanthemum plant, that disrupts the nervous system. This ingredient is mixed with both mineral spirits and petrocarbon oils that covers a wasps body and cuts off its oxygen supply. That double fisted punch acts to quickly knock-down a wasp while allowing the cyhalothrin to kill it. Plus, the oils will coat the nest, killing larvae while making the area undesirable for re-infestation.
If you want one of the most lethal wasp sprays available, check out CRC Wasp and Hornet Killer. It is made with two types of synthetic pyrethrins, tetramethrin and phenothrin, and both are bound together in a petrocarbon oil. Although accurate to only 20 feet, the killing power of this stuff may be worth the cost of admission right there. The extended trigger allows even gloved hands to use it effectively, and this may be one of the easiest spray cans to use. This is one of the more expensive wasp sprays on this list, but it is arguably the most effective as well.
From a name you know and trust, Raid Wasp and Hornet Killer 33 will get the job done. With a spray that is accurate to 22 feet, Raid is also made of two active pyrethrin ingredients, mixed in a petrocarbon oil base. This makes it highly powerful, and really, it's a horse apiece between the CRC brand and the Raid brand as to which is more effective. The Raid spray can uses a more standard spray nozzle, that may be a bit more difficult to aim than an actual trigger, but as far as killing power goes, Raid takes a back seat to no one. A decent spray distance, superior killing power and a name that has been the hallmark of insecticides for decades, that what you get with Raid Wasp and Hornet Killer.
The safest wasp killer for the environment is EcoSmart Wasp & Hornet Killer. Unlike other chemically made wasp killers, EcoSmart wasp killer is made with organic ingredients to get the job done. It uses peanut oil infused with phenethyl alcohol which, essentially, first coats a wasps body to prevent oxygen absorption with the peanut oil, while the alcohol additive gets the wasp toxically drunk. Realistically, if you want to humanely kill a wasp, this is probably the way to do it. It dies smiling the whole way. It is also mixed with peppermint oil to deter other wasps from attempting to recolonize the nest once it has been sprayed. Totally organic, safe for you and the environment, the spray only goes out to 18 feet, so you may have to spray and run before the wasps succumb.
If you want a little more bang in your natural and eco-friendly wasp killer, try Safer Brand Wasp and Hornet Killer. It is made with all natural pyrethrins, not synthetically made, which means they break down easily in the environment, yet they will do a decent job of killing wasps and wasp nests. The pyrethrins are mixed in with citrus oil, which coats the wasp body, depriving them of oxygen, and it also coats the wasp nest, making the area uninhabitable once it has been sprayed. It sprays out to 15 feet, so always wait until after dark and aim well. Although the natural based pyrethrins will do a good job of killing, they do not posses the speedy knockdown power of the synthetics, so once sprayed, leave the area and allow the pyrethrins to work.