I getting confuse.
People say tribute but I farm nothing with that.
If I do hordes I farm okey but not much.
Tested it last night.
NMD finishing anywhere between 2-8 minutes, was getting 300-600 on average about 475.
Tributes, finishing in about 3-4 minutes, getting 2k per run {I think my problem was that I wasn't paying attention to the end total that you get in one lump sum, in regards to my response above}
Infernal Hordes, 10-13 minutes and after getting the greater chest {do this so that you can get the free reroll scrolls for your items tempers} I'd get 1k-2500.
Nightmare Dungeons have the added chances to give you runes and Mythic uniques.
Tributes, I've never heard of a Mythic unique coming from any other than the one that has the added Mythic drop rate.
Infernal Hordes give you extra uniques/legendaries as well as gem fragments and obducites.
I found it best, towards the end of last night, to run 2 of each and keep cycling so that I'm not getting to bored. I did 2 nightmare dungeons, 2 tributes, 2 hordes and that felt fine. I ended the session last night with 21k obducites.