Since there has not been big complaints I believe that melee and ranged have been more balanced in T18 compared to the previous tier. My own, VERY subjective opinion about which one is better:
Hellfire Assault - melee
Iron Reaver - ranged
Kormrok - ranged
Hellfire High Council - ranged
Kilrogg Deadeye - melee
Gorefiend - melee
Shadow-Lord Iskar - melee
Socrethar the Eternal - ranged
Tyrant Velhari - ranged
Fel Lord Zakuun - melee
Xhul'horac - melee
Mannoroth - melee
Archimonde - ranged