Any 30 weight oil will be fine. Synthetic or conventional is up to you. I prefer 10W-30 for conventional, because it's harder to shear because of the better base stock. As far as synthetic, any synthetic will be fine. I like Castrol Syntec 0W-30. It's made in Germany, and is the only Syntec that is made in Germany. Very good oil.
Royal Purple is decent oil, but it sure as hell won't make it last longer than any other quality oil. Royal Purple is what is referred to as a 'boutique oil'. Not sold in real stores, and very expensive. You are better off going with Castrol, Pennzoil, Valvoline, etc. Same or better protection and a better price.