G&K or BNW?

So I got the vanilla version of the game, but I was just wondering that, once I decide to pick up an expansion, which one would be the best to get first. I just want to hear some personal opinions on the two.

If you only buy one, buy BNW -- it includes all of the G&K mechanics, plus BNW mechanics. All you lose are the G&K civs (except Ethiopia) and the G&K scenarios).

That said, check pricing. You should be able to find Civ V: Complete (G&K, BNW and all DLC except the latest map packs) for about the same price (or less) than BNW alone.