In Diablo II, it was widely accepted that repeatedly killing the Act bosses on Hell difficulty (along with a few other certain areas) yielded the best equipment. However, I remember recalling that the Diablo III game designers wanted to move away from that, and instead have people go through entire Acts to find gear. That being said, is killing bosses still viable? Is it better to just run around looking for Elite camps to kill?
Boss kills are still viable. However the best chance for the best item drops are now off Rare monsters and Champion packs that are found randomly throughout each Act. With the combination of that fact and the Nephalam Valor buff, Blizzard is attempting to provide the best item farming to be systematically clearing areas of Rares and Champions, finishing off with a boss (mainly because you know where they are) as opposed to repeatedly running straight to a boss.
A very good analysis of item farming is available here