When buying whole tomatoes for making pasta sauce I always get tomatoes packed in juice rather than puree. Those packed in juice are less processed and have a fresher flavor. Calcium chloride is sometimes used in the puree to keep the tomatoes from getting mushy. I prefer the flavor of the San Marzano variety but they are not always available packed in juice. The other culprit to watch out for is added sodium. There is a certain amount of sodium naturally in tomatoes so check the label ingredients to make sure none has been added.