I would think Mobil 1 0W-20 would probably be the #1 choice based on price and availability. However, there's nothing terribly wrong with choosing some other oil, and there are a lot of choices out there now.
Mobil 1 Advanced Fuel Economy in the '13 Outback now. Next oil change Pennzoil Platinum 0w20. PP was $10 less than M1 after rebate. Using Subaru oil filters on all.
First fill was Kendall GT-1 Full Synthetic w/ Titanium. Now, Amsoil XL 0w20.
I would run any API SN Full Synthetic 0w20 with confidence though.
I am only buying the Amsoil because I am 5 miles from the warehouse and wanted to run the Amsoil Severe Gear 75w90 in the diffs. Might as well get use of the Preferred Customer cost....
I would be more worried about what fluid is used in the diffs than in the engine. There seems to be a bigger difference in gear oil than engine oil.
Don't forget that NAPA has their Synthetic 0w-20 on sale for less than $4 a quart a couple of times a year. It's what I run, and is a clone of Valvoline Synpower.