Where do you plan to use the chainsaw? If there's any chance you might need to use the chainsaw indoors, don't get a gas model. Using any exhaust-emitting engine indoors is a serious hazard. On the other hand, if you might need to range far out into the woods, away from power outlets, you probably don't want a corded electric chainsaw, which keeps you tethered within the length of an extension cord.
What sort of cutting will you do? For heavy-duty logging, gas chainsaws remain the fastest and most powerful option. However, some electric and cordless models stand up well for lighter jobs, such as cutting firewood and clearing branches. Heavier-duty saws tend to be larger, as well, with bar lengths of 16 to 18 inches. However, experts stress that bigger isn't always better, as a longer bar can get in your way and increase the chances of kickback. For most home users, a 16-inch bar is more than adequate.
Do you have an alternate power source? If you need a chainsaw ready for emergency use and you don't have a generator to power it, a gas model is probably your best bet. Gas saws will keep running as long as you can put fuel and oil in them. Cordless saws can also function during a power outage, but you need a source of electricity to recharge them once the battery runs out.
Even the best chainsaw can't do its job without proper maintenance. For any type of saw, it's important to keep the chain sharp, well oiled, and properly tensioned. A chain that's too loose is likely to slip off, and one that's too dull or poorly oiled will be slow and more likely to kick back. Gas chainsaws require additional work, including filling the gas tank, storing extra gas properly, changing the air filter, and cleaning spark plugs.
A corded electric saw doesn't need a lot of tinkering, but it does need a heavy-duty extension cord — 14-gauge or even heavier 12-gauge — to provide the juice it needs for top performance. A cord with a built-in ground fault circuit interrupter (GFCI) adds a margin of safety.
Although you can do basic maintenance on your chainsaw at home, serious repairs require professional service, which you must usually get directly from the manufacturer. Schlepping the chainsaw to a dealer 30 miles away every time it breaks is a huge hassle, so if you're choosing between two similar saws from different brands, opt for the one that has a dealer or service center nearest you.