I was thinking about using Pennzoil Platinum 5w-30 in my Elantras. Hyundai's factory fill for the Sonata is Quaker State synthetic. I asked one of the guys here that used to work for Pennzoil, he told me that he likes the additive package for the Pennzoil better. Pennzoil, Quaker State and Shell are owned by SOPUS. You have to change your oil every 3mos to keep your warranty with Hyundai, I think you'll save a little bit if you go with the Pennz, Pepboys sells it for $1.99 with rebate a least once a month if not more often.
From everything I hear on this site M1 and Syntec are great products. You wouldn't go wrong with any of these.