Level 50+ Dungeon Order

[Archona]

As a fresh 50 your best bet for gearing up is:

Weapon : Grand Company Weapon -> Ifrit HM -> Moggle Mog -> Relic -> Zenith/Twintania/Extreme Modes
Armors: AF -> Darklight (CM/Praetorium runs) -> CT -> Coil
Belt/Jewelry: AK/WP stuff -> Darklight -> HQ Crafted (w Materia) -> CT/Ultima/Extreme Modes -> Coil

Basically your best bet is to chain run CM/Praetorium until full Darklight, maybe craft some jewelry or an armor piece if you're rich or just feel like it or depending on your class. You really don't need any gear from AK/WP/Hard Mode Dungeons at all anymore, people just run them for Mythology capping.

WP/AK now has ilvl 55 gear
Haukke Manor/Copperbell/Pharos Sirius have ilvl 60 gear
Darklight is ilvl 70.

HQ Crafted gear w full Melds is better than Darklight in most cases but the difference is miniscule and doesn't warrant the gil costs in my book, but don't let me stop you.

Order of difficulty:
CM/Praetorium -> HM Ifrit -> WP/AK/Copperbell -> Thornmarch -> CT -> Haukke Manor -> Pharos -> HM Garuda -> Ultima -> HM Titan -> Coil -> Extreme Modes