The best Tomato Salad uses fresh summer fruit.  We do not find anyone who disagrees, and the popularity of tomatoes in people's home vegetable gardens is evidence of this belief.  Living in a northern country like Canada, we look forward to spring, the planting of our tomatoes, and the anticipation of the first delicious tomatoes.  The taste of store-bought tomatoes does not compare with fresh garden tomatoes.   There is no comparison in the winter, in the summer, and not even if the tomatoes are locally sourced.  Why?

Why don't store-bought tomatoes compare favourably?  Store-bought tomatoes are refrigerated, and the refrigeration alters the taste.  Instead, tomatoes should be stored at room temperature.  In our family, this is common knowledge, witnessed by our taste buds.  Our experience is confirmed by scientific research.  Published by the National Academy of Sciences, contributed by Harry J. Klee, August 24, 2016, an article title begins with "Chilling-induced tomato flavor loss" and goes on to conclude:

In conclusion, we have demonstrated that chilling of ripe tomato fruits results in significantly reduced flavor quality. That reduction is associated with major alterations in contents of volatiles associated with consumer liking.

The full article is available for your reading and goes into detail about how this comes about.  For our purposes, use fresh tomatoes, and you do not need much else to make a great Tomato Salad.