Have read a little on this subject, and most believe that most of your engine wear happens at start up.
Therefore it is recommended that you go with a 5W-30 or even a 0W-30.
My vehicle is pretty new, so I went with Mobil 1 5W-30(can't do much better than M1).
However, if your vehicle is older, it may be harder to justify the expense of M1.
If you like to read, try bobtheoilguy. Think that's the site. Tons of info on oil.