Sonicare might be expensive but it leaves my teeth feeling cleaner. It's like having that perfectly smooth clean feeling after a dentist visit every day. No way I'll ever go back to manual scrubbing like some sort of troglodyte.
This is a miopic viewpoint. It may be good enough for you but not everyone's gums/teeth are the same. Some people are predisposed to gum disease and using a good electric toothbrush helps immensely.
Same goes for toothpaste, apparently. I asked my dentist once, and according to her the type or brand doesn't matter that much as long as it has fluoride in it.
We've been brainwashed by advertising to think that the paste and mouthwash are what matter. They help, yes, but brushing is what matters most. The toothbrush is not just an applicator.
That said, I personally find Sensodyne to work better than other brand's product for sensitive teeth.