Before buying a weed eater learn the main differences between them so you can make an educated buying decision.
Electric Weed Eaters vs. Gas Weed Eaters
Industrial Lawn Mowers
Before starting your search to find the perfect weed eater for your lawn care needs you will have to ask yourself a big question, "Gas or Electric?" Today a lot of power equipment comes in battery operated varieties so deciding on an electric over gas might make sense for you. As a general rule gas power weed wackers have more power to them, meaning they can handle areas with more and thicker weeds, while electric and battery operated weed eaters will loose momentum sooner and possibly will not be able of trimming larger yards with one battery. The key here is figuring out the size of your lawn and that might eliminate electric models right off the bat. For mid size and small yards an electric weed eater might be exactly what you are looking for. Electric weed wackers are typically weigh less than gas powered, and they are arguably easier to maintain, since you don't have to gas them up, or change out the oil.
Curved Shaft Weed Wackers vs. Straight Shaft Weed Wackers
Gas or battery operated weed eaters both come in straight shaft or curved shaft models. This means that either the base or shaft is straight throughout the length of the power tool, or curved at the bottom. The straight shaft models are typically used more by lawn care professionals and commercial landscaping companies. They tend to be able to reach more in hard to trim areas like under decks, near flower beds, along edges of the driveway and walkways, and also can be easily broken down and switched with other weed eater attachments such as leaf blowers, edger's, hedge trimmers, saws, pruners, etc.. The downside to the straight is the weight of them, and that is why the curved shaft models stepped into the arena. Curved shaft weed eaters are the trimmer of choice for homeowners because of the ergonomic design and light weight.
2 Stroke Engine vs. 4 Stroke Engines for Weed Eaters
Finally you will need to decide on the type of engine if you are going to go with a gas powered weed eater. Gas weed wackers come in either 2 cycle or 4 cycle engines. Synonymously know as 2 and 4 stroke engines. The biggest difference is the fuel type you will be using to start them, since for a 2 cycle weed eater the fuel will be a combination of oil and gas, where the 4 cycle weed eater takes only gas. 4 cycle weed eater are making a greater appearance in the outdoor power tool industry since they are known to be more environmentally friendly because they don't give off as much emission as the 2 stroke weed eater.
So there are the 3 main differences in weed wackers that you will need to know before buying one. Now its time to find the best deal (and I have heard the link below will get you the best bang for buck!)