Preferably tomatoes grown in volcanic soil, like San Marzanos.<p>It is well worth buying one can of several different brands of tomato sold in your locale, and making experimental taste-test batches with all other variables held constant.  With good quality inputs, you can beat the pre-made jarred marinaras <i>every single time</i>, using nothing more than a very basic recipe and a minimum of cooking skill.<p>Exercise caution.  Once you know how to make a good sauce, you will never be able to stand eating at Olive Garden again.