Rotella isn't approved for your engine anyway it's a 5w40
The owner's manual recommends 10w-40, 20w-40, or 20w-50 for warmer climates and/or "heavy duty" applications.
Anyways, I certainly wouldn't use Mobile 1 5w-30. It has been shown to perform extremely poorly in some turbo Subarus, not so much in others. Rotella is cheap, and it works.. but it's not one of the Subaru approved oils. Personally, I would use whatever full synthetic that meets Subaru spec and hasn't been proven to have problems (so just about anything besides Mobile 1 5w-30 and Royal Purple), that is, unless you're really hard on the car. Then I would use one of the more expensive brands.
For what it's worth, the second thread from the top in this forum covers oil choices, so this thread in unnecessary. http://www.clubwrx.net/forums/general-maintenance-troubleshooting-accidents/134324692-what-oil-should-i-use.html