another vote for sonicare.
our dentist saw a remarkable improvement with it 7 years ago and we've used it since. i think i've bought 4, lost 1, and 1 died after a few years, just get the "basic" model, autoshuts off after 2mins, what more could you want? i think the old basic was called the 4100 series or the e series, now it's relabeled the essence, and they give you the "angled" brush heads that work with the essence now (which are better than the straight to really get in there)
oh i also have the replacement heads on amazon 6month (cuz they say replace every 6 months) auto bill so i know when i get a toothbrush package in the mail it's time to replace, easy/peesy.