Peter is right, you should try the Alta Cucinas if you are unhappy with San Marzano's. When I visited Naples this summer I was shocked at how much better the canned tomatoes were than what we can get in the US. There was no acidic or bitter taste, and the fruit was sweeter with a richer flavor than I expected. I have come to realize that the vast majority of San Marzanos we get over here seem to be the bottom of the barrel. Purists might find the Alta Cucinas to have a different flavor profile, but I still think that they make a better pizza than most brands of SM. Stanislaus also makes some other products like the tomato strips that give you more usable fruit in every can. They have a very similar flavor to the Altas.
I am trying to convince an importer of Italian foods to bring the la fiammante tomatoes in to this country. These come highly recommended by a fellow forum member Marco who grew up in Naples. It looks like it will take over a year, but it might really happen. If so we will finally have some real San Marzanos here in the U.S. to take our cooking up several notches. Until then, just hang in there and stick to the Miur Glens, which are fine tomatoes. 6 in 1's are really amazing tomatoes for NY/American style sauces, but would probably not be too authentic for a Neapolitan style pizza.