Well it all depends on how you brush. I am a current dental student and I am told if your an awesome "toothbrusher" than theres no need for an electric toothbrush. If someone struggles to brush their teeth correctly, it's a great idea to use an electric toothbrush.
Another point is " what takes 4 minutes manually brushing is equal to 2 minutes of brushing with an electric toothbrush"
I, myself use a professionalcare Oral-B electric toothbrush (it was provided by the school, I would never buy on myself). What I like about this style is the timer, thats excellent for making sure you brush you teeth for a reasonable time. It is also a chargeable toothbrush, which is also a perk.
If your considering buying an electric toothbrush like this be aware of the price (which you probably already are) but as well as the price of new "heads" which is pretty steep as well. Hope i helped a bit. :)