Basically there are only 2 types of motorized toothbrushes that you should look at and they are the Sonicare and the Oral-B.  I used the Sonicare for about 1.5 years and thought it was working well until my dentist told me that I was starting to have receding gums.  While I cannot blame the Sonicare, in my opinion I think the Oral B is gentler on your gums.  There is also a "mild" setting which is easier on your gums which is not an option on the Sonicare.