Sooner or later, most or all vehicle manufacturers will prefer 5w20 for all drivers. 5w30 seems like ideal and norm. 0w30 and 5w20 is hot right now. 0w20 is for the cars of the future, coming near to a dealer lot near you in 2015.
My 2000 Subaru is spec'ed for 5w30 but I'm using MC 5w20 since mid Oct. Runs fine and hasn't used any oil in ~4000 miles. I have a stash of Mobil 1 0w20 that I may use next.