"Tomatoes in a can are always better than fresh tomatoes because they have already been cooked (trust me)."

Completely true, but not just because they've been cooked: tomatoes in a can were usually picked ripe, so they actually taste like, you know, tomatoes. Fresh tomatoes from a grocery, even "vine ripened" ones, aren't truly ripe and will almost always be lacking in flavor.

I make my own salsa, and I typically use a mix of fresh and canned (diced) tomatoes: the fresh ones for the proper texture, the canned ones for flavor. It's not ideal, but it's better than either alone. The ideal solution would be to grow my own, but I inherited my mother's black thumb.