I was checking where the best relics come from for 7.1.5. Eye of Azshara drops the Storm relic that increases Lava Burst damage. Black Rook Hold drops the Frost Relic that increases Lava Burst damage. If you want to farm Mythic+ try those two for the best relics.
Would also recommend Court of Stars since it also has a Lava Imbued relic in addition to Infernal Writ which is now pretty high up on the trinket list. Also has the necklace half of the Chrono Shard set.