Man. Thats a tough one. Claws of ahamkara With the final melee perk on in your subclass skill tree your melee charges your super AND your grenade. Also with embrace the void perk in the voidwalker skill tree your grenade damage charges your super. So 2 melees creates a strong feedback loop for you if you run your perks like i mentioned. its exotic perk also works for both subclasses. And i love having 2 flame chrges. Obsidian mind. You can run the perks mentioned above and kills on enemies in pve charge your super, and your super charges your super. So its a tough call. If you swap subclasses alot then go claws of ahamkara. Having 2 grenades and melee charges on sunsinger is super fun. If you stick with voidwalker a lot then go obsidian mind.