In our office,  we are asked this question many times a day.  Our other dentist,  hygienists and I all offer the same answer:  Buy what you like to use, what works  and what you will want to continue to use.  Two brands seem to stand out:  Sonicare and Braun Oral-B.  We have used them all and they all work well. Right now most of us are using the Braun Oral-B Triumph.  It has a round head with little plastic flaps that seem to get in between teeth well.  Sonicare Brushes I have used also get my teeth clean.  Sonicare is using a brush that moves back and forth, vibrating rapidly.  Some people prefer this. I have personally not liked the "sonic" brushes because the tickle/vibration is uncomfortable to me.
I also have used the less expensive Oral B Deluxe for a while and liked it.  I would never choose a brush because of bells and whistles like an LCD readout, multiple speeds, etc.  Just make me one that holds it charge, gets the plaque off, feels good in my mouth, does not break and is easy to throw in the suitcase. That's really all I ask.
There are also non-rechargeable and very inexpensive battery operated brushes in the tooth care aisle of the drug stores.  I suspect that some of them must work well, even though  I have come to trust and like the higher-priced rechargeable  for myself.  Even with an electric brush,  you have to take the time to keep it charged and to actually use it,  contacting on all areas of all the teeth for a couple minutes during brushing.  And, of course, you still need to floss.