You are always better of using synthetic regardless of the change intervals.
For one thing in general the Synthetic will help clean your engine, might be good to even do a couple 3000 mile oil changes with synthetic just for that reason alone.
I would go with a 5W30 mostly, if you happen to live in an environment that is like 9+ months out of the year HOT then 10W30 would be fine.
I would pick a date out of the year to make that oil change day unless you drive more than 5000 stop and go short trips a year or 7000-8000 highway miles per year.
Use the best quality oil filter you can find.
There honestly isn't any valid reason to use petroleum oil, the cost difference is negligible and the Synthetic is better oil under any circumstances.