Hi,
I'm a dentist based in Europe and that's a question many patients ask me. The answer is: Both brands produce equally effective toothbrushes. Although there have been more than 200 clinical studies comparing those 2, most of them are conducted by Braun and Philips, so they are biased in their own direction. Main difference is in technology behind them. Some people prefer oscillating (rotating) technology of Oral B and some prefer sonic (fast vibrating) technology from Sonicare line.
In my opinion oscillating toothbrushes are less sensitive to brushing technique, that's why I prefer Oral B toothbrushes when I'm buying some for my parents and grandparents. Advantage of Oral B is also the price. Similar models from both brands cost about the same, but brushing heads from Oral B line are much cheaper.
For a better understanding, here are 2 videos comparing brushing technique of each one:
Oral B:
https://www.youtube.com/watch?v=HkdgyXHEboE
Sonicare:
https://www.youtube.com/watch?v=gjoR91BmJJQ
And here's an in-depth comparison of both brands:
http://www.bestelectrictoothbrushhub.com/oral-b-vs-sonicare-comparison/
I will be checking this thread daily if anyone has any question.
