They are both designed to help support your coil springs and improve the ride by leveling your vehicle. Which is better will depend your personal preferences, your vehicle and how much you are planning to tow, haul or support.
The main advantage coil SumoSprings have over suspension air bags is you can install and forget them. There are no air lines or air pressure to worry about. Once you install them, you are done. They are easier to install and are great for lighter loads and tongue weights.
Coil air bags like Firestone Coil-Rite and Air Lift 1000 are preferred by a lot of our customers because you can adjust the air pressure: increase while towing and decrease when not. They are rated with a 1,000 lbs. capacity and will give you more flexibility.