what oil is safe?

What does everyone here use for oil? I have been told by many people that todays oil is bad on engines with flat-tappet cams. Due to the lack of zinc. Since my 318 was rebuilt I have been using mostly Valvoline. One friend of mine said he uses one quart of Shell 15w-40 Rotella with every four quarts of conventional oil. Another friend of mine said to use one quart of mobile one synthetic with four quarts of conventional oil. What do you guys use in your muscle cars? I have put over 1,000 miles on my car since the rebuild. I don't want to ruin the engine just becuase of the oil. Any help is appreciated. Thanks