Farm 2* full on. That way you can benefit the system the most. Also try to keep all 4* (no point swapping CandD with Agent Venom - keep both). Other uses of HP? I occasionally buy daily deal on vaults (so I know what I might get). Also sometimes on shields in PvP (mainly to protect my score at the end of event or to make sure I can hit 900 and grab the 4* cover I really need). And from time to time we have special vaults that give great rewards (like around anniversary, so in September/October I guess). It makes sense to keep some HP for that occasion.I would not waste HP on H4H store. The price is outrageous. But if you can champion Rhulk when he is there the next time - might be worth it (or just make him your Bonus Hero and he might show up sooner). No point saving for 10 or 40 packs. They tend to disappoint.