Civ 5 Gold Edition OR Civ 5 Gold & Brave New World

Just buy Gold Edition + BNW

Through Steam trade you can save a few bucks.

I'd say go for gold, more time to get used to the new stuff it adds then go for bnw.

Buy it with both of them. BNW is totally worth it!

My install path was like this:
Free Civ V from GMG voting.
BNW for about 8 bucks from GMG sale
Gold upgrade from Steam for 5 dollars

After you have BNW, Gold just adds maps and civs.

BNW. You MUST get BNW. You can skip Gold, just get BNW.

When you have BNW, all Gold is giving is few civilizations and scenarios. All good stuff from Gold is already inside BNW.

If you are new to Civ then just start with vanilla civ and get familliar with the gameplay. You can still purchase G&K and BNW later, by the way both of them are great and add a lot to the gameplay.