Choosing the right chain saw depends on both who you are and what you want to do with it. A chain saw that is too big or heavy for you to properly control is an accident in the making. A smaller chainsaw that affords better control will work a lot better for you that a larger saw that you have to struggle with or rapidly fatigues you. For most people, a saw with a 14 or 16 inch bar is ideal. Remember, it is not the weight of the saw that does the cutting, a heavy saw will only fatigue you, it will not do a better job at cutting wood.
Most experts also recommend a gas powered saw over an electric one.
The downside of the gas powered saw is that it is generally heavier. For the very casual user, a second hand chainsaw is a cheaper option to a new saw. When buying a used chainsaw, make sure that it has all the more recent safety features. In the event of kickback, this brake presses against your hand and stops the chain. Most saws manufactured after 1980 have a chain brake.