The nice thing about the Necrobear is that it has nodes that give you more titan souls, which means that it helps compound on itself the more you invest into it. It also gives very meaningful raid damage bonuses, which can help you complete higher raids to earn more card rewards and raid XP as well. And it's also one of the most efficient uses of diamonds for main game damage.
There are still many great equipment sets to focus on, but the main ones are really Treasure Hunter to help you complete all other sets, Celestial Enchanter that's the most efficient set in the game, and The Great Traveler sometime before or when you enter Transcendence. The other sets are strong, but you will also naturally complete them over time through random equipment drops and your crafting shards