Like here is the ranking of the Arch Devils in AD&D considering their HP and Armor
Bottom Pit Fiend (13 Hit Die, Ave 45 HP, AC -3)
Princess of Hell Glasya (69 HP, AC -2)
Duke of Hell Titivilus (86 HP, AC -2)
Duke of Hell Bael (106 HP, AC -3)
Duke of Hell Hutijin (111 HP, AC -4)
Duke of Hell Amon (126 HP, AC -2)
Archduke Moloch (126 HP, AC -3)
Archduke Geryon (133 HP, AC -3)
Archduke Mammon (139 HP, AC -3)
Archduke Dispater (144 HP, AC -2)
Archduke Belial (154 HP, AC -4)
Archduke Baalzebul (166, AC -5)
Archduke Mephistopheles (188 HP, AC -6)
King of Hell Asmodeus (HP 199, AC -7)
Asmodeus also had the power to deal damage equal to his HP in a large areas 3 times a day, so he is for sure on top.