I don't believe there is a 20W-50 Mobil 1. Perhaps you are thinking of Mobil's petroleum based oils.
Everybody here has their own favorites and rationale for choosing it.
My personal choice would be 15W-50 Mobil 1 changed every 3,500 miles or six months (whichever comes first).
Frequent changes of name brand oils that meet the viscosity recommendations in your owner's manual should be fine.
Naturally, you should use OEM filters.