In pothole heaven (New England and New York) I'd go with 18" wheels. You run too much risk of tire and wheel damage with19" wheels. The greater the sidewall, the less risk. If you still prefer the look of 19" wheels, buy the tire insurance.
2010 535i xDrive Sport Wagon (April 2009): Deep Sea Blue / Cream Beige / Sport, Premium, Cold Weather Packages
2011 335i xDrive Coupe (April 2011, European Delivery): Le Mans Blue / Oyster-Black / M Sport, Premium, Convenience Packages