Modern rechargeable toothbrushes can have so many features that you'd never use them all, particularly if you're a single person. If you have a family then it may be worth getting a toothbrush with all the bells and whistles as then there's sure to be a cleaning mode and speed which will suit everyone's teeth.
If you have reasonably good teeth with no special cleaning requirements and you don't suffer from heavy plaque formation, the best electric toothbrush for you will probably be one with just a daily clean mode, a cleaning timer and battery charge indicator. This will be a fairly basic model which can be bought reasonably cheaply but will still last you a good long time.
However, if your teeth have heavy staining or plaque builds up easily then you may want a toothbrush with special deep clean and whitening modes which you will get when you buy a more sophisticated and expensive model. The Oral-B SmartSeries 4000 and 5000 models both have these features.
For people with sensitive teeth the best electric toothbrush will be one which has a special sensitive setting and they may find that a toothbrush with a pressure sensor is helpful.
If speed is what you're looking for then a sonic toothbrush is the one for you. One of these will produce between thirty thousand and forty thousand brush strokes per minute and the sound waves generated as well as the vibrating water molecules will give your teeth and gums a real workout. Because of their technological advances, these toothbrushes are currently quite expensive.
If you want a choice of brush heads with different functions such as flossing, whitening, care of sensitive teeth or care of braces, be sure to choose a toothbrush brand which offers the ones that you want and which all fit one base unit.
If you go on short trips a lot, then the best electric toothbrush for you will be a rechargeable one which holds its charge with normal use for up to two weeks. You will also need a base unit with a battery charge indicator so that you know how much charge is left.
So, as with any product purchase, it's horses for courses and the best electric toothbrush for one person isn't necessarily the best for someone else.