I'll be waiting for BE. Here's why:
Civ V was launched in a horribly unfinished condition. My wife and I both pre-ordered the games and essentially ended up with $100 in coasters for a year. Yup, it took a whole year before the game was patched so you could play Multiplayer without problems. Singleplayer was fixed about 3-6 months after launch. The biggest issue with singleplayer was a problem with the game's code - it actually caused video cards to overheat! In addition, many features that players came to love from Civ IV: Beyond the Sword were absent in Civ V, and most people felt that the devs pulled out facets of the game in order to sell them later. Now, four years later, Civ V is finally to the point where it's great to play - Brave New World gave lots of gameplay additions and (FINALLY) brought back aspects from Civ IV. So I'm going to sit back and see how BE ends up.
That said, if you are on the fence about a turn-based strategy game, I highly suggest you strongly consider purchasing Civ V while it's on sale now. Either get the base game for $7.50 or get the complete edition for $16.50. The complete edition is far superior to the base game, but both are great ways for you to find out what you think about Civ style games with a smaller investment.
Holding the fort on old games that play the same as the new ones, minus the $400 price tag.