Like many here, I will stick with Mobil 1 0W-40 Euro Formula.
Not sure what your climate is like, but here in SF Bay Area (summer time) my car is liking the 5W-50 better. The engine runs just a bit smoother on that.
There's nothing wrong with 0W-40 though, other than that ExxonMobile changed the composition and you can no longer easily get the good "euro formula" stuff. It's all "FS" something or other and lost the BMW LL-01 rating. It still meets Porsche A40 though.
The 0W-40 will do better than 5-50 if you're not pushing your car hard very often, I believe. Better cold start protection in exchange for a little less effective high temp viscosity. I just run my car hard enough on back roads that I feel I'm better off with the -50.
We actually had to step my wife's MINI down to 0-30. The computer got mad after 2500 miles on the 0-40 that my family was stocking for all our cars. Now we're all on mostly different oils, darn it.