I would prefer Vasoline 5W50 as it seems the best I've tried. I have tried Shell 5W40, Mobile 5W50 on my BMW 318iS and S320L. The difference Vasoline gives me is most impressive - smoother, less friction. But the fact is that you have to change the oil more frequently (probably 5000 miles at most as it "fades out" or becomes more sticky a bit earlier.)
By the way, it is the least viscous one and viscousity is not relative to the degree of protection. Just my opinion...