Item drops

Im stuck at Nightmare 3-4, have really weak armor, have no gems so the only option is to farm drops. Im just curious if boss drop rate is higher then regular mobs drop rate? or its the same? Maybe some tips what level to farm with good drop rates.  I have a Tier 8 rare Sword that is ok, but Tier 5 Legendary sholders, tier 7 helm, Tier 5 magic amulet and a tier 6 legendary ring. I die in 10-15 hits