Electric toothbrushes have a lot of features. Some even have built-in-timers so you know how long to brush for. The moving bristles help to break up any plaque build-up. Electric toothbrushes stimulate the gums and teeth with different configurations of the bristles. They are also expensive and it is costly to replace the heads.
Manual toothbrushes when used properly, work very well. With manual toothbrushes, you have to do the work, so technique is very important. The brush should be at a 45 degree angle to the gum, in order to get inside the gumline. You should move the brush in circular motions, and you should brush your teeth for at least three minutes.