1. Lawn Size. With an electric trimmer, you are limited to the length of your extension cords and availability of a power outlet. There is the option of a cordless, battery-operated trimmer, but these have their own limits considering the charge may last less than an hour, at which point it will need to recharge for several hours. For smaller yards, this is a non-issue. But, large yards nearly always require a gas-powered trimmer, as they aren’t bound by a cord or battery life.
2. Noise Tolerance. It’s no secret that gas-powered trimmers are much louder than electric, and many require hearing protection. This makes sense, of course, considering all this power is generated by an internal combustion engine. If you prefer to work quietly, electric trimmers are the clear winner over gas.
3. Terrain. Electric trimmers are quieter than those with gas motors, but they are also less powerful. For trimming the basic lawn’s grass and weeds, this difference likely won’t matter. Both electric and gas trimmers are perfectly capable of slicing through grass. But if you’re dealing with thicker brush and shrubbery, an electric trimmer isn’t going to pack quite enough punch for you. A gas trimmer will be the better choice in this case.
4. User Strength. Since gas trimmers have an engine, they are noticeably heavier than electric trimmers. Corded electric trimmers don’t have an engine or even a battery, which results in a significantly lighter piece of equipment. Also, gas trimmers are started with a pull-string (like a lawn mower), and may take a couple of pulls to engage. Electric trimmers are turned on with a switch. For the elderly or other users who may have less physical strength, an electric trimmer is a more manageable option.

In summary, here are some pros and cons of gas trimmers vs. electric trimmers:

Gas Trimmers

• Fewer Movement Limitations (Cordless)
• More Power
• Can Handle Rougher Terrain, Thicker Brush

• Louder 
• Heavier
• Regular Maintenance Required