Doing the rares will definitely be your most efficient route. IoD rares are somewhat rarer than most other wilderness areas, they have maybe a 1:5 spawn rate except for the Glabrezu who is up every time. Excluding the Glabrezu, I usually only get 2-3 rares per run.
Definitely stay away from Stone Jaw. He is incredibly tough. Fight him once for the experience of doing it, and that should be enough of a lesson about why not to keep doing it for farming purposes.
However, it would definitely not kill you to do the actual quests. Heroic IoD items are REAAAAAAAAAAAAAAAALLY good, basically making most drops from Ravenloft, Sands, and other pre-Sharn areas completely obsolete.