It's your town and you should decide what makes it pretty.
Personally I don't like cosmos that much but if you like them and want them in your town nobody should be able to say anything about it. Except praises of course.
I love cosmos! I have about equal amounts of cosmos, roses, lilies, and tulips around my town in different sections. (Pansies and violets are left out because they don't come in black and white, which is the theme I have going, but I do like those too.) The only flowers I don't like at all are carnations, they just look really odd and flat next to the other flowers.