Depends on what you are trying to find.
If you just want the standard end game items like Shako, Tgods, Ravenfrost, etc. then you should be farming the act bosses and superuniques as much as you can.
If you instead are trying to find the gg high ilvl items like Death's web, Griffons, Fathom - or socketables like Archon plates, Eth polearms - or high runes - then you should be farming the lvl 85 areas.