Don't be fooled that canned tomatoes are not as good as fresh tomatoes. If done correctly, they are picked at the height of their ripeness and packaged immediately to preserve their precious flavors.
That said, the buyer should beware, because there is a huge difference between brands!
Maybe because I toured Campania in 2009 and tasted the real deal, perhaps because I am a daughter of Benevento, or more likely that I am a snob - I must share my findings.
All San Marzano tomatoes are not created equal!
I admit that I thought I was buying the good stuff for years until Gina, a well-informed clerk at my local market, pointed it out to me recently. Once I made the comparison I never looked back.
The can on the right, the one that is quite ubiquitous in supermarkets and fine food emporiums is not authentic. They are grown right here in the good 'ol USA and packaged in New Jersey.
The Italbrand can on the left is one of the stars of my pantry. The tomatoes are darker than the domestic ones and are packed with less water and salt. These juicy San Marzanos come from Naples and are grown in the rich soil near Mount Vesuvius. They get bonus points for the coveted DOP designation. DOP or PDO stands for "Protected Designation of Origin." The acronym identifies an Italian product whose expert preparation, production and processing occurs in a specific geographical area of Italy.
All these details are important when I am hankerin' for marinara sauce, and I'm flinching now as I type marinara, because the origin of the word means "from the sea" and not the simple red sauce we have all come to know and love. But I digress...
I adapted my own marinara recipe after dining at Arturo Iengo's legendary Ristorante Pascalucci in Benevento. He advises to "smoosh" your tomatoes with your hands. That's important. My other favorite tip is to add a rind from Parmigiano-Reggiano.
(I freeze the rinds every time I finish a wedge just for this purpose.)

Marcy's "Smooshed" Marinara

Saute onions and garlic in a combo of olive oil and butter, whatever ratio you like, about five minutes.
Add smooshed San Marzano tomatoes to mixture.
Add cheese rind.
Simmer 20 -30 minutes, longer if you are more patient than me. Remember the rind is salty so be careful when correcting with salt.