My experience was like Jodi's. The San Marzano's did much better with the grafted tomatoes, and the Brandywines did better with the non grafted plants. I also used Morton Hybrid and there was little difference. However the reason I used the grafted tomatoes was to see if they would do better in my garden which suffers from a fungus and kills the tomatoes after the first crop. I believe it is Verticillium wilt, however, other plants that are susceptible to Verticillium like peppers and egg plant are not affected. The plants initially looked much better with the grafted ones vs. un-grafted, but the results were as I mentioned above. If anyone knows of a grafted tomato that is completely resistant to Vericillium please let me know.