The Volt has a longer battery range, which means that if you're running in the cold with the heat, it will still have a respectable battery range - that chews range in a hurry, figure 50-70% of summer battery range in the winter, depending on temps and number of people in the car (heated seats are a lot more efficient than heating the cabin, but heated seats do nothing for kids in carseats in the back).
I'm a little biased, but 'd rather have a mature Chevy product (second gen of the Volt, several model years into production) than a fresh Hyundai, just in terms of engineering solidity.