While the Katana is the obvious best choice for your Ground General, it's not easy to come by. In the meantime you can use either the Ares or Achaemenidae Sword as they have identical Ground buffs. The only difference is the debuff.
The Freedom Hero Armor has Ground Attack, Defense, and HP buffs, making it the best choice. Although the Furinkazan Armor isn't too far behind, it just lacks a Ground Attack buff.
If you have neither available to you, Fearless Ares or Achaemenidae works just fine. I would lean towards Achaemenidae because if I'm going to make a Fearless Ares Armor piece, it's likely going to end up on a Sub General instead.
While the Furinkazan Boots are the obvious choice here, not every will have access to them right away. The Courageous Ares and Achaemenidae become your next best choices. Which one you pick really comes down to whether or not this slot will get you a set bonus. If this slot doesn't get a set bonus it really comes down to whether or not you want to burn 800 badges for the Ares.
The Furinkazan Helmet is considered the superior option because HP is more important than Defense. But if you don't have it, the Freedom Hero Hat is a nice backup. If you have neither, the Courageous Ares Helm will work in the short term
Weird one here, the Fearless Ares Pants are actually the best in slot for Ground. This is works well if you have another Ares peice for the set bonus. If you need to complete a Furinkazan set bonus, and this is the only chance you have, it's not that far behind.
The Furinkazan Bracers are the only choice for your Ground General. The only other option that gives you Ground buffs is the Fearless Ares Ring which is already a bitch and a half to unlocked. And even then it's not that good!