Let's see. I definitely notice a difference between zucchini and yellow squash. And I had a yellow zucchini this spring. Only thing I could tell between that yellow and the common green was that the skin was thicker/tougher on that yellow. (Buckingham variety). So I doubt Buckingham will be back next year.
On the greens, maybe Cavilli is a tad more flavorful. It does have a creamy texture and I do like it very much. But really not much difference in flavor between varieties.
But I don't have the most best taste buds. I know people told me different eggplant varieties have differing taste. Well, I cook them and I could never tell ANY difference at all except in thickness of skin. No taste differences I could pick up. And yet there are definitely supposed to be taste differences. Just that I could pick up on it.
But I tend to think that once cooked, a zucchini is a zucchini.