How big is your property? If you have a lawn or garden that extends less than 100 yards from the most convenient power source, you may be able to use a corded hedge trimmer. However, if your outdoor space is larger or involves some odd obstacles, you'd be better off with a battery-powered or gas trimmer.
Do you want to
cut branches thicker than ½ inch? Most hedge
trimmers are recommended to cut up to 3/8-inch branches. If you need to cut
something a half-inch wide or more, you'd be better off with a
How often do you plan to use your hedge trimmer? If your plants only require occasional trimming (a few times per year), then a cheaper electric or cordless model makes a lot of sense. For more frequent jobs, spending the extra money for a more durable gas trimmer may save you time and even money in the long run.
Measure your garden. How much distance do you have between your hedges and an outlet? If it's less than 100 yards, a corded trimmer is an option.
Try it in the store. The weight of the trimmer engine and the balance of the blade make a difference in how easy it is to use and handle. Try the trimmer in a store (go through the motions without actually powering it up) or rent a model you're considering to make sure it's right for you.
Check the warranty. Users report having durability issues with hedge trimmers - even from some of the most respected brands - sometimes right out of the box. Check to see what the warranty covers and for how long.