Most users aren't willing to spend $89 or $99 on a case, but if you are, the Samsung and Mophie are hands-down the best options around. They offer more features, a great design, quality battery, and protect the phone at the same time.
Those who are more concerened about battery life than protection, should consider the Ruky 4,500 mAh Galaxy S7 battery case from Amazon. It's a snap-on case with minimal protection, but promises to pack a massive battery under the hood to increase usage by nearly 15 hours.
The Ruly has a built-in kickstand, but certainly isn't the best looking case in the world. Eiher way, it will add tons of juice for long hours for those that need it.