Many professional gardeners don't like electric or gas-powered hedge trimmers because they can chew up leaves and leave behind mangled edges and browned tips. Hand shears give you a better feel for how a shrub grows and where to cut. Still, gardeners faced with a lot of shearing rely on good power trimmers for large jobs.
For best results, you'll want to keep your tools in shape, too. To avoid damaging leaves, hone cutting blades at least once a year. Take power shears to a pro for honing; hand clippers are easy to sharpen with a beveled-edge file. Clean them after each use with soap and water or, if blades are sticky with pitch, a solvent-soaked rag. Then wipe down with a penetrating oil such as WD-40. Store them in a scabbard or on a wall hook to keep them clean.