Regular oil is fine, and what came in the engine out of the factory, I recommend synthetic based on driving conditions. I am in a area with high pollution and horrible driving conditions, on both extremes. The majority of my customers regularly have either long trips in lots of traffic, or very short trips without letting the oil fully warm up on each trip, and synthetic copes with this much better.
Be it regular or synthetic in the crankcase, I strongly suggest 5k mile intervals. With the amount of carbon build up issues that these engines have(PCV failures, fouled throttle body blades...) keeping the oil clean is well worth it and will keep these issues at bay. Obviously both regular or full syn. can last, and lubricate properly for longer then 5k miles, but oil does a lot more then just lubricate, and its other properties (cooling, build up...) do get compromised when the oil is dirty.