Chaos isn't going to be a tournament winning list no matter which Mark you bring. Khorne Daemonkin, however (a book combining the forces of Khorne - daemons and traitors both) can be a very mean army, and is (funnily enough) Khorne.
Pick the one you like the aesthetic and fluff for; otherwise, you'll never have the momentum to finish an army. It's doubly true for Chaos Space Marines, as your list isn't going to be spectacular no matter what Mark you bring, so follow your heart.
Pick the one you like the aesthetic and fluff for; otherwise, you'll never have the momentum to finish an army. It's doubly true for Chaos Space Marines, as your list isn't going to be spectacular no matter what Mark you bring, so follow your heart.