Don't farm green hunt.
Here's why:
Attack set is worse than Destruction set in terms of damage output.
HP is easy to build with gear substats. Health set is less useful than Immunity or Resist set.
Defense set is very niche. Very few units have skills that directly scale off raw DEF.
You already start with an ATK set and an HP set. You can buy another set with $10. You can buy a third set from the Arena Shop. Two full sets of Health set gear will equip SIX units! That's enough for everyone.
Full Guide Coming Never (tm)