As you have gotten a LOT of very fine replies, I won't redundantly repeat them over and over.
What little they didn't say (so far) is:
- There seem to be four different power sources for a snow blower.
1) Two cycle engine, mix gas and oil
2) Four cycle engine, oil in the crank case
3) Electric
4) Power take off from garden tractor
- Sizes are rated in inch of cut (width) and also in horse power. More HP means more power, but burns gas/ electric faster. You get the job done faster, and I doubt that a big unit actually uses more gas, over the course of the year.
Several years ago, I got bombed in snow, and for the first time tried out an electric snow thrower I'd found on the curb a couple years before that. It worked so well, I was completely impressed.
Since then I bught a two cycle gas mixer, which is about 3 HP. I just simply totally love it! I snow blow my own driveway, the driveway for the elderly lady across the street, and some for the truck driver (who got hurt in a wreck) across the street. As well as a little trim work for a couple other neighbors.
Buying a snow blower doesn't obligate you to clear your neighbor's driveway, though. You may choose to if you wish.