2 energy for 100 diamonds 3x20=60 for duel of champions for higher ranks faster meteorite is good and you get more artefact essence at 6fights. 150for daily reduced cost key and you upgrade venom spawn/ commander too. This is on average best way. But not always i change it sometimes and depends on level. Almost noone does it this way...then some waste covenants on commander ...when you can get commander and upgrade it this way with other huge benefits. And yes you get some keys free but it's way slower.
2 energy for 100 diamonds 3x20=60 for duel of champions for higher ranks faster meteorite is good and you get more artefact essence at 6fights. 150for daily reduced cost key and you upgrade venom spawn/ commander too. This is on average best way. But not always i change it sometimes and depends on level. Almost noone does it this way...then some waste covenants on commander ...when you can get commander and upgrade it this way with other huge benefits. And yes you get some keys free but it's way slower.