For me it came down to head size. I have a small mouth (can you hear DH laughing??

) in fact the endodontist had to use kiddie-size instruments. The Sonic is too big for me because of its rectangular size. The smaller, round head of the Oral B was much nicer.
I have the dual-speed brush with the two minute timer and I love it. It holds a charge for about a week which is nice for short vacations.