If you're going to ride an ATV, you need a helmet it is that simple. But buying a helmet, given the vast amount of choices out there today can be a daunting task for anyone.
You have already heard how a helmet is the number one piece of safety equipment to wear when you're riding your ATV and how a helmet not only protects your head, it makes for a safer ride by cutting down on noise from wind so you can actually hear other sounds more clearly.
Make sure you get a full face helmet that is DOT and/or Snell certified. Don't waste your time with helmets that are not certified, Additionally full face helmets do not replace the need for goggles but a full face helmet can save your from getting your face sprayed with debris and at the speeds an ATV can kick up debris, it can feel like pepper spray when it hits your face at high velocity.
Also, make sure that the helmet you choose to wear when riding your ATV is comfortable. It should have adequate padding and should fit snugly but not too tight around your head. A neck roll that hugs your neck is another good feature that most newer generation helmets have. Make sure the chin strap fastens well and the helmet stays in place. Shake your head a little bit to confirm this.
The more EPS your helmet has the better. The EPS is what actually absorbs the force of an impact so the more you have the more protected you are if and when an impact happens.
Make sure it's certified, make sure it has good fit and you'll be ready to ride your ATV safely and with a great helmet!