Reddit mentions of Sid Meier's Civilization V: Gods and Kings [Download]

Can anyone help me out here? I didn't see a link on the main landing page, but I found these two:

BNW - Amazon - $14.99

G&K - Amazon - $14.99

I just bought vanilla during the last Steam sale (this game is amazing BTW)... what's the difference between these two expansion DLC's? Are there others? Is one better than the other? Do they both add different content, should I buy both?

Since the link has a list of all the games on the sale, here are the individual Civ games:

• Civ V
  
  
• Civ V: Gods & Kings
  
  
• Civ V: Brave New World
  
  
• Civ V: Complete Edition (PC) and Civ V: Complete Edition (Mac) (NOTE: the other games/expansions have PC/Mac versions available to choose on the page, but the Civ V Complete Edition does not, so pick the link that goes with your system)
  
  
• Civ IV
  
  
• Civ IV: Colonization
  
  
• Civ IV: Warlords
  
  
• Civ IV: Beyond the Swords
  
  
• Civ IV: Complete Edition
  
  
• Civ III: Complete

Brave New World (7,50USD) http://www.amazon.com/Sid-Meiers-Civilization-Brave-Online/dp/B00CYOHL48/ref=pd_sim_vg_1?ie=UTF8&refRID=19TF7DQWT3R1223S9TBX

Gods and Kings (7,50USD) http://www.amazon.com/Sid-Meiers-Civilization-Kings-Online/dp/B0085O6NG8/ref=pd_sim_vg_1?ie=UTF8&refRID=0QV4BYCD02JEMB6QYXXW