Yes, I know there are a hell of a lot more than these, but I only know the ones that are reasonably mainstream in Canada (or more specifically, Alberta).
Personally, my favourite is Cadbury, though Lindt is very close. The worst, in my opinion, is Hershey, which tastes tolerable at best (best being the reese cups).
What are yours? Also, are there major manufacturers in your country that I missed?