Look for a deadman control so that the machine stops when you release it. No one wants anything other than snow entering the auger.
Electric starts can get you going quickly...you don't want to be warmed up on a cold winter's day due to the exercise required by a recalcitrant pull starter.
Storage is an important consideration for many. Some electric models come with folding handles to make these machines even easier to fit into a crowded garage.
See if the auger has a blade designed to break up accumulated ice or snow. This feature will be welcomed when you have a base of ice.
Make sure you will be able to adjust the chute easily.
It's all about power...can the machine do the job? If you envision multiple snows of 18 inches in the winter, go for the larger nine horsepower engine. Keep in mind that these little guys can move...make sure you can handle the power as they wade through the heavy snow. If however you don't get above four inches the two stage snow blower may not be necessary...
Does your driveway sport a wide girth? The fewer passes you make with the snow blower the happier you will be, so pick a machine that will match the job. If it is just a short, thin path to the car or the garage, you might find an electric model with a thinner cleaning path will do just fine. But any serious driveway is going to need one of the big boys.