I don't know about the fastest, but I prefer the Level 50 dungeon and expert dungeon roullette along with Vanu quests (because until you max out Vanu there are some days you can get 1/3 of an unidentified with them) and it's certainly more fun than running Alexander variations 800 times. Shoot me in the face if I do that. I'm doing 10 of each floor, but I certainly find the Alex grind the most boring.
I'm at about 20/80 and I'm not even trying with just the roullettes/beast tribes and 10 runs of A1.

I'm leveling my crafting so I'm not farming anything outside of my dailies.