Comparing the two is a lot like comparing the same phone from two different companies. Although they look different, they are practically the same. If you compare two models from the same class, one from Mercedes and one from BMW, you will find they; have the same options, the same safety features, the same handling and come at around the same price. Plus they both come from the same German luxury engineering. So all in all it boils down to a physical appearance preference. Mine would be the Mercedes SLR McLaren but if that wasn't an option it would be any of the BMW's M series. They handle amazingly, are fast as hell and are beautiful pieces of machinery.