Everyone you ask will state a different interval and oil type. Of course, most dealers will say "every 3000 miles" which is outdated.
This is what I do when I buy a new vehicle: I keep the factory conventional oil for 4500-5000 miles & then do the first oil change with conventional oil. By 10K miles, the rings should be seated and then, starting with the second oil change, every oil change is with full synthetic at 7000-7500 mile intervals. I stock up when its on sale for half price or buy-one-get-one free with a free K&N wrench-off oil filter.
With gas at $4, the slight improvement in fuel economy when using synthetic might pay for the higher cost of the synthetic oil.