It depends a little bit in your gear level and therefore what you can easily farm.
On my seasonal Wizard I'm easily killing T13 Rifts so I waltz through a bunch of them to build up my Grift keys, at around 3-5 minutes per run, including a set of Nemesis bracers, which spawn extra elites and therefore extra deaths breaths.
Doing that will also net you a bunch of yellows and therefore crystals, but I think I get more from Kadala while I'm spamming GR60s to increase Legendary gem levels for Augments. Burning through Blood shards to look for upgrades will net you 36-40 yellows per 1000 shards maybe? And I think at GR60 it's 250-300 per run, so you get a lot.
farm only whites and convert them to yellow mats , i only farm yellows this way , try to gather only whites in your rifts, try to play paladin quest in act5 story mode to get 9 10 whites in 1min (dont forget not to end quest), or farm those whites in north section of leoric castle (skeleton archers and shields on the walls) over and over, and then convert your whites to yellows from cube.