If you do a lot of cooking, you might have noticed that most recipes call for canned whole tomatoes, which in some cases you have to go on to chop or dice yourself. Isn’t it OK to just buy pre-diced or -crushed tomatoes to save yourself some time?
In a word: no.
Whole tomatoes are, in fact, the only tomatoes where you know you’re getting exactly what the can says: whole peeled tomatoes. Period. (Although be sure to buy ones packed in juice, not puree, which tend to be less flavorful.)
Diced tomatoes may seem like a shortcut, but they’re actually treated with calcium chloride to help keep them rigidly in the dice shape. Not only is this kind of gross, but they won’t fully meld with the other ingredients. In some cases, like soup or chili, this is fine, but in others it just leads to weird textural issues.
Crushed tomatoes may seem a little safer, but according to Cooks Illustrated, the USDA regulates the “appearance and consistency” of all canned tomatoes except crushed. That not only means that companies are free to use their crappiest tomatoes to go in the crushed cans, but the ratio of actual tomato meat to juice varies wildly from brand to brand. And if you’re buying on a budget, the can you’re likely to buy is probably not going to be at the favorable end of the ratio. Buy smart! Buy whole!
The $35 a Week Project 
This is good to know! I’ve been using diced tomatoes as a shortcut for a long time, but I think I’ll go back to whole ones. Occasionally I splurge and buy San Marzano tomatoes, and they’re wonderful, but definitely expensive at over 3 times the price of a brand like Unico. BTW, you’re right about the textural issue of diced; they’re mostly okay but occasionally there are some tough little dice in there. Thank you for the new perspective on canned tomatoes!