I'd say BMW all the way having owned 4, an X3 2d, 318M Sport Convertible, 335iSE, and a 335MSport (current). The BMW is a drivers car, and yes, it is expensive to own and maintain, however the engineering behind them is superb. If the car is <2years old the BMW warranty is for 3 years, and besides, these things are built like tanks, the only things that need changing are tyres, wipers etc.
As I say, they are built to last whereas I find that the Jap cars, though well spec'd as standard feel cheap. BMW / Merc are prestige cars, but I find Mercs don't handle very well.
Hence I vote for the 530.
My 2 cents.